McCain, too, changed course. In the final weeks of the campaign, the Arizona senator struck a more negative tone and, along with vice presidential running mate Gov. Sarah Palin of Alaska, began attacking Obama's relationships and judgment.
In the third and final presidential debate, McCain assailed Obama for his relationship with 1960s radical William Ayers and his campaign began aggressively using auto-dialed calls -- known as robocalls -- to voters to relay negative messages, frequently focusing on the Democrat's experience and readiness for the White House.
That strategy didn't seem to achieve the desired effect, with voters responding in polls in the race's final weeks that they were turned off by the negative ads and attack tactics.
The economy is nationally the overwhelming issue for voters who cast their ballots in today's historic presidential election, according to early exit polls.
Despite the possibility of Obama becoming the nation's first black president, the turnout of black voters as a percentage of the national vote was 13 percent, just slightly higher than in 2004, according to early exit polls.
The economy has long dominated the campaign, and voters' concerns became heightened when the major banks and credit markets needed a massive federal bailout to avoid a fiscal catastrophe.
Four in 10 voters said their family's financial situation was worse than it was four years ago, and eight in 10 are worried the current economic crisis will hurt their family finances over the next year.
In an indication of how intensely fought this campaign had been, both candidates kept holding large rallies and television interviews even as voters swarmed to their polling sites. In the past, presidential candidates have halted their campaigns on Election Day.
McCain voted early in Phoenix before heading off for some last-minute get-out-the-vote efforts in New Mexico and Colorado, two states where the GOP presidential pick had trailed but hoped to pull out narrow victories.
"I promise you if I'm elected president, I will never let you down," an energized McCain told a crowd in Colorado.
"I think we ought to hear one more time 'drill, baby drill,'" he cheerfully suggested and the crowd obliged with the campaign's chant.
After voting at a Chicago school, Obama spent the morning campaigning in Indiana before returning to Chicago to conduct television interviews broadcast via satellite to the swing states of Florida, Pennsylvania, Colorado, Virginia, Ohio, North Carolina, Nevada and Missouri.
Obama voted with his two young daughters in Chicago before he plunged into a final round of campaigning in Indiana.
"I voted," the Democratic presidential candidate said, holding up the validation slip he was given after turning in a ballot at the Shoesmith School in his Chicago neighborhood.
Obama voted at the same polling station as William Ayers, the former 1960s radical who became a flashpoint in the campaign when Palin accused Obama of "palling around" with a domestic terrorist.
Sarah Palin, McCain's running mate, voted in her hometown of Wasilla and then joined McCain in Phoenix to watch the results.
After voting, Palin noted that the result would be historic, implying that the voters would elect either the country's first black president or the first female vice president.
"It bodes so well the progress our country is making," she said.