Sen. Hillary Clinton, D-N.Y. has battled back from the political brink by defeating Sen. Barack Obama, D-Ill., in the crucial voting states of Texas and Ohio, where the former first lady fought hard for Latino voters and the white, working class voters who have typically supported her in earlier primaries.
The headline battles in delegate-rich Ohio and Texas were considered crucial primary contests that could cement Obama's hold on the Democratic presidential nomination, or help Clinton continue to fight on for her party's nomination.
In her victory speech in Columbus, Ohio, Tuesday night, Clinton claimed a comeback.
"For everyone here in Ohio and across America, who's ever been counted out but refused to be knocked out and for everyone who has stumbled but stood right back up, and for everyone who works hard and never gives up, this one is for you," Clinton told a cheering crowd of supporters.
"This nation's coming back and so is this campaign!" Clinton said.
Clinton Claims a Comeback
A Clinton adviser said the Ohio win would be enough for Clinton to fight on to the next big primary in Pennsylvania on April 22, nearly six weeks from now — the longest stretch of time without a contest in the nomination season.
"I dont see anyway she doesn't go forward now," a Clinton adviser told ABC News' Eileen Murphy. "We were outspent massively. Ohio clearly augurs well for Pennsylvania. We'll see what happens in Texas but in my view there's no argument for getting out," the adviser said.
Obama: 'This Is Not The Future We Want'
In a subdued speech to supporters Tuesday night in San Antonio, Texas, Obama maintained he is still ahead in the delegate count and slammed his Democratic rival.
"No matter what happens tonight, we have nearly the same delegate lead as we did this morning, and we are on our way to winning this nomination," Obama said.
"This is not the future we want. We want a new course for this country. We want new leadership in Washington. We want change in America," Obama told supporters. "John McCain and Senator Clinton echo each other in dismissing this call for change."
McCain: 'The Contest Begins Tonight'
On the Republican side, Senator John McCain, R-Ariz., swept the March 4 GOP primaries in Ohio, Texas, Rhode Island, and Vermont and now has the 1,191 delegates needed to become the Republican presidential nominee, according to ABC News' delegate count.
"I am very very grateful pleased to note my friends. that tonight we have won enough delegates to claim with confidence, humility and a sense of great responsibility that I will be the Republican nominee for President of the United States," McCain told supporters Tuesday night.
"The contest begins tonight," he said to cheers and applause.
At McCain's election night party headquarters in Dallas, a huge banner reading "1191" hangs alongside hundreds of red, white, and blue balloons.
McCain will meet Wednesday with President George W. Bush, who is expected to endorse the Arizona senator at an event in the Rose Garden at the White House.
Conceding the race, former Gov. Mike Huckabee, R-Ark., suggested his candidacy gave a voice to the millions of Christian evangelical voters who supported his campaign.
"Not only have we fought the good fight and finished the race but more importantly, we have kept the faith. I would rather lose an election than lose the principles that got me into politics in the first place," Huckabee said.
Clinton Wins Women in Ohio, Blue-Collar Workers
Breaking a 12 contest losing streak, Clinton won Ohio with 141 delegates at stake and won Rhode Island, with 21 delegates up for grabs. In Ohio, Clinton won women and won white men, with huge margins among women and men without a college degree, according to exit poll results.
Obama, meanwhile, racked up a win in Vermont's Democratic primary -- a win that was expected by both candidates and credited to that state's sizeable population of liberal and Independent voters who have typically gone for the Illinois senator.
In Vermont, Obama beat Clinton among senior citizens as well as among white women, two of her core groups. His focus on "change" prevailed over "experience" by nearly a 40-point margin.
But it was Clinton's hold on low-income, low-education Democrats and women -- key demographic groups in Ohio that could help her win in Pennsylvania over a month from now.
Clinton had the most at stake coming into the race, facing pressure to cede the nomination battle if she didn't win both Texas and Ohio, with a combined 370 delegates up for grabs.
Even former President Bill Clinton said she must win both states to stay in the race, although a new ABC News/Washington Post poll shows Democrats by a 2-1 margin think the former first lady should fight on even if she only wins one or the other.
Some influential Democrats suggested Clinton should drop out of the race if she wasn't ahead after Tuesday's votes.
"We have to have a positive campaign after Tuesday. Whoever has the most delegates after Tuesday, a clear lead, should be, in my judgment, the nominee," New Mexico Governor Bill Richardson, a Democratic superdelegate himself, said on CBS's Face The Nation Sunday.
Outside a Houston elementary school, the voting site for a heavily Hispanic area, Clinton indicated Tuesday morning she planned to stay in the race.
"I don't pay attention to what people are saying," Clinton said. "This is a long process as some of you have heard me say before," she told reporters. "My husband didn't get the nomination wrapped up until June. That has been the tradition — that it usually lasted longer."
Asked about the ABC News/Washington Post poll which seems to support Clinton's perspective, she replied, "Never underestimate the intelligence of the voter."
Hispanic, Blacks Key Texas
Latinos turned out in big numbers in the Texas Democratic primary, accounting for a record 30 percent of voters, up from 24 percent in 2004, according to preliminary exit poll results.
Latinos went 63-35 percent for Clinton over Obama. Clinton also won white women in Texas by 19 points while white men split evenly between Clinton and Obama. The Illinois senator won 85 percent of black voters in Texas, who accounted for 19 percent of Democratic primary voters in the Lone Star State.
Many Texans took advantage of early voting rules; early voting is expected to account for 50 percent of the total Democratic primary votes, according to the Texas Secretary of State's office.
But earlier Tuesday Clinton expressed dismay at the peculiar voting rules in Texas, where Democratic delegates are allocated through a combination of the results from primary votes and caucuses. Texas apportions delegates in a complex system that may yield Obama more delegates from expected wins in Texas' big cities, while giving Clinton less delegates for expected wins in Latino areas along the border.
"When the dust clears, we have to ask some tough questions," Clinton told reporters in reference to the Texas voting rules, arguing that the limited window to appear at a caucus makes it difficult for particularly working class voters to participate.
Heated Race Turns to Delegate Count
Obama went into Tuesday's contest with a 110-delegate lead, according to the ABC News delegate scorecard.
Clinton has a very serious math problem. Almost regardless of what happens Tuesday and in the few remaining states left to vote, she will be behind Obama in delegates when the last primary vote is cast in Puerto Rico in June. That makes the role of superdelegates all the more important.
The Obama campaign issued a statement Tuesday suggesting Clinton must make a significant dent in Obama's pledged delegate lead -- an unlikely event given state polling and the Democratic Party's proportional system for according delegates.
"The Clinton campaign said this race was all about delegates and that they would be tied or ahead by morning," said Obama spokesperson Bill Burton in his statement. "But despite the 20-point lead in Ohio and Texas that Senator Clinton had just two weeks ago, we will still be well ahead in delegates tonight and they will have failed at achieving their plainly stated goals."
Obama: Media 'Bit' on Clinton's Complaint
Obama began election day in Houston at a livestock and rodeo exhibit, posing for pictures and climbing on a tractor.
En route to San Antonio, Obama and his wife, Michelle, strolled to the back of the plane, telling reporters he thought the race is "tight" and described Clinton as a "tenacious" candidate.
Obama said he was surprised the media "bit" on her "complaining about the refs" -- referring to Clinton's complaint during a debate in Ohio that the media was giving preferntial treatment to Obama.
Obama Accuses Clinton of 'Kitchen Sink' Strategy
With her candidacy at stake, Clinton has turned up the heat on Obama in recent weeks, questioning his national security and foreign policy credentials and his position on trade.
The Clinton campaign launched a television ad on Friday asking voters to consider which candidate they would want to pick up the phone in a time of crisis.
"It's 3 a.m., your children are safely asleep. Who do you want answering the phone?" it said.
The Clinton campaign also held a conference call to urge reporters to probe more deeply into Obama's relationship with Tony Rezko, a Chicago real estate developer who is currently on trial in connection with extortion allegations.
On Tuesday as voters headed to the polls, Clinton communications director said Obama's campaign hasn't been transparent with Ohio voters about a conversation Obama's senior economic adviser Austan Goolsbee had with a Canadian official in Chicago.
A Canadian government memo reports Goolsbee told the Canadians Obama's anti-NAFTA rhetoric should be taken more as political positioning than an articulation of policy objectives. The Obama campaign and Goolsbee dispute the Canadian memo.
In Ohio, NAFTA is blamed for job losses.
Obama has accused Clinton of employing a "kitchen sink" strategy, but Clinton's campaign appeared to succeed in putting her rival on the defensive.
Clinton communications director Howard Wolfson argued Tuesday Clinton is the best candidate ready to be commander-in-chief on "Day One" and deal with a flagging economy, not Obama.
"We are not going to nominate someone to run against McCain who has not passed the commander-in-chief test and not passed the steward of the economy test," Wolfson said in a conference call with reporters.
The Obama campaign held a competing conference call Tuesday disputing Clinton's national security and foreign policy creditials, pointing to her vote to authorize President Bush to use force in Iraq.
On Tuesday the Clinton campaign accused the Obama campaign of election day chicanery in Texas, a charge the Obama campaign denied.
The Texas Democratic Party said they have received concerns from both the Clinton and Obama campaigns about the other side improperly padding their caucus vote totals by getting primary voters to fill out sign-in sheets all day long rather than waiting until the primary polls close and the caucus process formally gets underway, but Texas Democratic Party officials tell ABC News they do not have any proof of wrong-doing.
Some polling stations in Ohio stayed open later than expected because they ran out of ballots. Election officials in Texas and Ohio said voter turnout was high, depite rain, sleet, and flooding in some areas of Ohio.
After her wins in Ohio and Rhode Island Clinton appears ready to fight on, urging supporters to bolster her campaign warchest and donate money online.
Clinton will appear on network televsion news programs Wednesday morning.
The Democratic rivals battle next in Wyoming on March 8, where 12 delegates are at stake, and in Mississippi on March 11, with 33 delegates.
The next big prize is Pennsylvania on April 22 with 158 delegates up for grabs. Many believe that if no clear winner can be determined before the final primary vote is cast in June, the two historic, formidable candidates could fight all the way to the party's Denver convention in August.
ABC News' Kate Snow, David Chalian, Rick Klein, Eileen Murphy, Andrew Fies, Kevin Chupka, Karen Travers, Gary Langer, Teddy Davis, Eloise Harper, Lauren Pearle, and Sunlen Miller contributed reporting.