Barack Obama urged wavering supporters not to give up on their dreams of change - or on him - as he accepted the Democratic Party's nomination for president in what promises to be a tough race against Republican Mitt Romney.
Mr Obama used his nationally televised speech closing out the Democratic National Convention to try to revive the excitement that powered his first run for the presidency.
With just two months before election day, Mr Obama needs to win over undecided voters, especially those who had been swayed by his inspiring message of hope and change in 2008, but now feel disillusioned after years of economic weakness and persistent political bickering.
"The election four years ago wasn't about me. It was about you," he said. "My fellow citizens - you were the change."
He said the American people were the ones responsible for accomplishments on his watch, such as overhauling healthcare, changing immigration policies and ending the ban on gays in the military. If they turned away now, he warned, "you buy into the cynicism that the change we fought for isn't possible". "Change," he said, "will not happen".
Mr Obama built on the message Democrats delivered throughout the convention: that America is on the road to recovery while Mr Romney would revive failed policies, cutting taxes for the rich and slashing programmes that give regular Americans a chance for a more prosperous future. "If you reject the notion that this nation's promise is reserved for the few, your voice must be heard in this election," he said.
Republicans, who nominated Mr Romney last week, argue that America's high 8.3% unemployment rate is proof that Mr Obama's policies have failed and that the president's spendthrift, big-government policies have hurt business and caused the federal deficit to soar.
The two candidates are locked in a tight race. Polls show that Mr Romney, a wealthy businessman and former governor of Massachusetts, is seen as the better candidate for improving the economy, while Mr Obama is viewed as more likeable and having a better understanding of everyday Americans.
Mr Obama's speech marked the climax of the three-day convention. First lady Michelle Obama highlighted the first day, talking about her husband's humble roots and compassion for those living through tough times. Bill Clinton, the popular former president who led the United States during years of prosperity, gave a rousing speech on Thursday, vouching for Mr Obama's economic policies and urging Americans not to turn back to Republicans.
Preceding Mr Obama was vice president Joe Biden, who was formally re-nominated. Mr Biden proclaimed in his acceptance speech that "America has turned the corner" after experiencing the worst economic crisis since the Great Depression.