Election Day often comes down to the results of a few crucial battleground states where key electoral votes can hold the key to the White House.
In 2000, that battleground was certainly Florida. In 2004, much of the election seemed to hinge on the results in Ohio.
This year, the campaigns are focusing their time and money on several critical states where the race is hard-fought. But with the election looming just a week and a half away, Democratic candidate Barack Obama has taken an increasingly commanding electoral-vote lead in eight critical battleground states that could decide the presidency.
ABC News has looked at several factors to assess how those electoral votes may fall on Election Day -- including reporting from the campaigns themselves, national party officials, outside groups, House and Senate party committees, state parties and polls. Analysis shows that Republican candidate John McCain's support in these states -- all of which went to George W. Bush in both 2000 and 2004 -- may not be enough.
On Wednesday, a top Republican campaign official told ABC News' George Stephanopoulos on the condition of anonymity that the Obama campaign is on a roll.
"This is the greatest ground game they've ever put together," he said. "It's scary."
Eight Key Battlegrounds
Eight states that could go either way -- Ohio, Florida, Virginia, Colorado, Nevada, Missouri, Indiana and North Carolina -- hold 111 of the 270 electoral votes needed for either candidate to win the presidency.
Whether those red states will turn blue is yet to be determined, but according to the latest polls, Obama has a 52-45 percent advantage in those battlegrounds. States like Indiana, Missouri and North Carolina, previously leaning in McCain's favor, are now considered toss-ups.
With polls showing Obama leading in Colorado and Iowa, McCain needs to hold all the big states Bush won in 2004, plus capture a John Kerry state like Pennsylvania in order to win the presidency.
If this year's map breaks the way it did in 2004, then Obama would need to win only one of the red battleground states where he leads or is tied in polls with McCain. A victory in Virginia, Florida or Ohio would net Obama enough electoral votes to win the White House.
OHIO: 20 Electoral Votes
According to a Wednesday CNN/TIME/Opinion Research poll, Obama is up 50-46 in Ohio.
Voters in Ohio have selected the eventual winner in the past 11 presidential elections, and no Republican has ever won a presidential election without winning the state.
This election, economic discontent could be a decisive factor in that decisive race. With half a million Ohioans out of work -- the state's highest unemployment rate in 16 years -- and with the state also tallying the third-highest home foreclosure rate in the country, the latest ABC News/Washington Post poll of Ohio finds that the economy is the single most important issue to the state's registered voters.
In that environment, Obama could find success based on support from voters in the state's hard-hit industrial belt in the northeast, as well as in the heavily Democratic Cleveland metropolis. Conversely, the McCain campaign is working to secure the Republican strongholds of southeastern and southwestern Ohio, where white, working-class voters supported Sen. Hillary Clinton over Obama in the Democratic primary. McCain and VP pick Sarah Palin also appeared together in Green, Ohio, outside of Akron, this week in their first joint rally since Oct. 13 when they joined forces in Virginia Beach, Va.
Stark County, where Canton lies, and Franklin County, home to more than 50,000 students at Ohio State University in Columbus, are two key counties to watch.
Since the last presidential election, there are also indications that Ohio voters could be growing increasingly wary of Republican leadership. In 2006, the election of Democratic Gov. Ted Strickland ended a 16-year Republican hold on the governor's mansion.
Democrats won races for U.S. Senate, attorney general, secretary of state and treasurer. Ohio Republican Rep. Bob Ney also resigned his seat days before Election Day 2006, after pleading guilty to conspiracy, making false statements and receiving favors from lobbyist Jack Abramoff.
Early voting began in Ohio on Sept. 30, and the Ohio secretary of state's office projects that 25 percent of Ohio voters could vote before Election Day.
FLORIDA: 27 Electoral Votes
The race in Florida is essentially tied, according to a Wednesday Mason-Dixon poll.
In an effort to secure the battleground, the McCain camp has devoted millions of dollars and staffers to the state in recent weeks. On Thursday, the candidate began a trans-Florida bus tour, stopping in swing counties across the central part of the state.
"We're doing well in Florida," McCain said at a recent stop in Plant City, Fl., reported ABC News' Bret Hovell. "We're gonna win here in Florida, and the great Governor Charlie Crist assures me of that, and he's never been wrong."
Connecticut Sen. Joe Lieberman, an independent who has also been working Florida extensively for McCain, and McCain's vice presidential pick, Gov. Sarah Palin, have drawn tens of thousands of people at recent Florida events. McCain is also hoping the state's older population and a large number of veterans will help him win.
Since being soundly defeat in Florida by Clinton in the primary, Obama has made up ground. Obama campaign manager David Plouffe estimates the campaign will spend $39 million on its effort to win the state, and Obama is trying to energize black voters, whose participation in Florida elections usually lags.
There are also more than 650,000 more registered Democrats than Republicans in Florida, as of Oct. 1, although Republican strategists dismiss the advantage. They say Democratic registration has outnumbered Republican registration in the past two presidential contests as well, to no avail. They also contend that young Floridians simply don't vote.
Still, since going to Republicans in 2000 and 2004, Florida has changed. No longer experiencing a building boom, the state is now ranked No. 2 in the nation in home foreclosures and is facing its first recession in 16 years. In a dramatic shift, there are also now more registered Hispanic Democrats than registered Hispanic Republicans in comparison with 2004.
Florida Republicans say Tampa and Orlando hold the key to a McCain victory on Election Day. The Florida Panhandle will also be critical, with big cities including Tallahassee, Pensacola and Panama City. Obama is counting on a big turnout in Miami-Dade County.
MISSOURI: 11 Electoral Votes
As Missouri goes, so goes the nation. Missouri has backed the winner in every presidential election since 1900, with one exception: Adlai Stevenson won the state in 1956 but lost the presidential race to Dwight Eisenhower.
But some say the state's bellwether status could be in jeopardy this year. A strong Obama supporter, Missouri Sen. Claire McCaskill, has been advising Democrats on how to increase support in Greene and St. Charles counties, both critical to McCaskill's win in 2006, as well as in other rural areas.
Obama, meantime, drew massive crowds of between 75,000 and 100,000 people each to this month's rallies in St. Louis and Kansas City, urban areas usually filled with Democratic votes compared to the rest of the rural, traditionally Republican parts of the state.
The Obama campaign is also focused on increasing turnout in Columbia, home to 28,000 students at the University of Missouri, as well as in Jefferson City.
An Oct. 1 Time/CNN/Opinion Research poll showed a tight race in Missouri, with Obama ahead 49-48. In a Sept. 9 poll from Time/CNN/Opinion Research, McCain led 50-45.
Like so many states, the economy is the dominant issue for voters in the Show-Me State, according to officials from both campaigns. The summer announcement that St. Louis-based Anheuser-Busch was being sold to Belgium's InBev sparked concern about job losses and may feed into voters' concerns about jobs moving overseas, trade agreements and the general state of Missouri's economy.
The office of Missouri Secretary of State Robin Carnahan anticipates that voter turnout could be half a million more than in the 2004 election.
INDIANA: 11 Electoral Votes
Indiana has not voted for a Democrat in a presidential election since 1964, but a Big Ten poll released Wednesday found Obama was up 51-41 in the state.
Officials from both parties say a competitive Democratic primary in Indiana in May could explain why Obama is doing so well in the polls. The tight primary race excited Democrats and bumped up voter registrations. Obama also had dozens of events in the Hoosier State and established a ground game for the primary.
McCain has had just one event in Indiana since wrapping up his nomination in early March -- a speech on July 1. Obama has had several in that time, including a large rally in Indianapolis on Oct. 8.
On Thursday, Obama held another rally in Indiana before leaving for Hawaii to visit his ill grandmother.
Strategists say the key area to watch in Indiana is Indianapolis and its suburbs. For Obama, pockets of opportunity may be found in the northwest corner of Indiana, close to Chicago, where towns like Gary and South Bend tend to vote Democratic. He also hopes to find support in Perry County in the south, as well as in Bloomington and West Lafayette, home to Indiana and Purdue universities.
NORTH CAROLINA: 15 Electoral Votes
According to a Wednesday Time/CNN/Opinion Research poll, Obama is up 51 to 47 in North Carolina.
But Republicans are confident that North Carolina remains fundamentally conservative. North Carolina hasn't voted for a Democrat for president since 1976, and it is conservative Democrats, not liberal ones, who often win local elections in the state.
Still, the state's large black population, large college communities and growing cities -- especially in the middle of the state and among high-tech workers in the Research Triangle Park -- suggest opportunity for Democrats on Nov. 4. Democrats have also seen a surge of new voters registering in North Carolina for their party. More than 292,973 of the state's new voters are Democrats and only 60,157 are Republicans. And 192,948 Independents were added to the rolls this year.
As a result, McCain is working hard to bolster the state's enthusiasm for the Republican ticket. In recent weeks he has increased the number of paid staff in North Carolina and visited Wilmington last week, marking his first visit to the state since May. Republicans also think Obama's support for gun control could decrease his chances.
Both Republicans and Democrats in North Carolina believe that a Democrat needs about 40 percent of the white vote in the state to be successful. Obama's pick for vice president, Joe Biden, campaigned in North Carolina on Thursday in hopes of gaining support.
COLORADO: 9 Electoral Votes
As of Sept. 30, data from Colorado's secretary of state shows why the state could be home to a tight race on Election Day: Democrats make up 32.1 percent of state voters, Republicans comprise 33.7 percent and 34.2 percent are categorized as other.
Still, Colorado has gone Republican in 12 of the past 14 elections for president.
But powered by a growing Hispanic population and the growth of households headed by professionals with advanced degrees, Democrats have gained significant ground in recent years in Colorado.
In 2004, Democrats won control of the state legislature. They also flipped a House seat and replaced retiring Republican Sen. Ben Nighthorse with Democrat Ken Salazar.
In 2006, Democrats expanded their majorities in both the state House and state Senate, and Democrat Bill Ritter won the governor's office. Democrats also won a majority of the congressional delegation by capturing an open House seat when Republican Rep. Bob Beauprez made an unsuccessful run for governor.
Hoping to capture that momentum, Democrats chose Denver as their convention location this year. But for Obama to carry Colorado, he will need to win over unaffiliated voters who live in the Denver suburban counties of Arapahoe and Jefferson. He will also need to hold down McCain's numbers in the rural parts of the state.
NEVADA: 5 Electoral Votes
With the single exception of 1976, Nevada has been won by the victor of every presidential election since 1912.
McCain has the potential to do better with the state's Latino voters than the typical Republican because of his work with Democratic Sen. Ted Kennedy on comprehensive immigration reform.
Still, the Arizona Republican faces other significant challenges in the state. He claimed 13 percent of the vote in the Republican primary caucuses in January, compared to 51 percent for Mitt Romney. He has showed continued support for storing nuclear waste at Nevada's Yucca Mountain. And his work in the Senate to outlaw betting on college sports puts him on the unpopular side of an issue that is important to many Nevadans.
Now McCain's battle to beat Obama in Nevada is also complicated by the Libertarian Party's nomination of former Republican Rep. Bob Barr, of Georgia, who could be seen by some as an alternative to the GOP ticket. Barr's vice presidential candidate, Wayne Root, is a professional handicapper from Las Vegas.
Democratic registration gains in the state also make the Obama campaign optimistic about its chances. Since January 2008, when Democrats held an early, attention-grabbing caucus in Nevada, they have enjoyed a 4-to-1 registration advantage over Republicans.
Obama was ahead by 5 percentage points in Nevada, according to a Time/CNN/Opinion Research poll released Wednesday.
Democrats are strong in Clark County, home to Las Vegas, while Republicans do best in the rural parts of the state. Reno's Washoe County, where Bush won 51 percent of the vote in 2004, will likely be the key area to watch.
VIRGINIA: 13 Electoral Votes
Virginia has gone to the Republican presidential candidate in every election since 1964, but this year the Illinois senator is in a good position to turn the red state blue. Virginia has been in this critical position before: In 2006, Democrat Jim Webb took down incumbent Republican Sen. George Allen in a tight, hard-fought race that tipped the balance of power in the Senate to Democrats.
A Time/CNN/Opinion Research poll released Wednesday showed Obama up 10 percentage points, while a Mason-Dixon poll had him up 2.
"I feel like we got a righteous wind at our backs here," Obama said Wednesday in Leesburg, Va., ABC News' Jake Tapper and Sunlen Miller reported.
The booming Northern Virginia region bordering Washington, D.C., is largely seen as the root of the shifting demographic. The population in those counties is exploding as more liberal voters move into places like Arlington and Alexandria from Washington, D.C., and Hispanic and immigrant populations grow quickly in Fairfax County.
Obama is expected to also gather votes in Richmond, Norfolk and Charlottesville, home to the University of Virginia.
McCain, meanwhile, has support in rural counties, especially in concentrated areas in western and southern Virginia. Conservative, evangelical Christian areas, such as the southwest corner of the state, home to Jerry Falwell and the conservative Liberty University, could also help carry the Republican nominee.
But while the Obama campaign has invested extensive money and resources into winning the state, Virginia political analysts said they believe McCain has not put in the time necessary to seal the win.
Obama and his running mate, Joe Biden, the Delaware senator, have held more than twice as many events in Virginia as McCain and Palin. The Obama campaign has about four times as many paid staffers there as the McCain campaign.
Democrats could also be propelled by the fact that there have been nearly half a million new voter registrations in Virginia since Jan. 1 -- the largest surge in voter registration in state history. Nearly 40 percent of those new voters are under the age of 25.
Both campaigns say the race for Virginia could come down to the Hampton Roads region in the southeastern corner of Virginia. A large military population in Virginia Beach, Norfolk and Newport News could be fertile ground for McCain to pick up votes. The region is 45 percent African-American and the Obama campaign is counting on a high turnout there. Other critical counties for both campaigns include Loudon and Prince William counties.
Both parties caution that there is a good chance for ticket-splitting with the presidential and Senate race.
ABC News' Teddy Davis, Tahman Bradley and Jennifer Parker contributed to this report.