Democrats turned to a hero of the past, Bill Clinton, to boost the shaky re-election prospects of Barack Obama, with the popular former president from the prosperous 1990s assuring worried Americans that he feels "with all my heart" that Mr Obama is steering the country to an economic recovery.
Mr Clinton, in a rousing address to a television audience of millions, formally nominated Mr Obama as the Democratic candidate in what is expected to be a tight race against Republican Mitt Romney.
Immediately after Mr Clinton's speech, delegates at the Democratic National Convention made the nomination official in a state-by-state roll call vote.
Mr Obama's acceptance speech tonight will mark the climax of the three-day convention, though Democrats have abandoned plans for Mr Obama to deliver the address at a large football stadium, citing weather concerns.
Democrats have used their convention to push back against Republican claims at their gathering last week that Mr Obama's devotion to big-government solutions has stifled the US economy and swollen the national deficit.
Democrats have countered that Mr Romney would go back to the economic policies that led to a recession, helping the wealthy while harming the poor and middle class.
Mr Clinton, who formally nominated Mr Obama as the Democratic candidate, followed through on the theme.
"If you want a you're-on-your-own, winner-take-all society, you should support the Republican ticket," Mr Clinton said.
"If you want a country of shared prosperity and shared responsibility - a we're-all-in-this-together society - you should vote for Barack Obama and (Vice President) Joe Biden."
Mr Clinton said the Republican campaign argument is "pretty simple: 'We left him a total mess, he hasn't cleaned it up yet, so fire him and put us back in'."
He said Mr Obama has "laid the foundation for a more modern, more well-balanced economy".
After the speech, Mr Clinton was joined on-stage by Mr Obama, who made his first appearance at the convention. The former president bowed, and Mr Obama pulled him into an embrace as thousands of delegates jammed into the convention hall roared their approval.
Mr Clinton was a striking choice for one of the convention's prime speaking slots.
He has had a checkered relationship with Mr Obama, who ran against Clinton's wife, Hillary, in the 2008 primaries.
The styles of the presidents are opposites: Mr Clinton is outgoing, emotional and chatty, while Mr Obama is cool, meticulous and reserved.
Whatever the past differences between presidents current and past, Mr Obama and his top aides looked to Mr Clinton as the man best able to vouch for him when it comes to the economy, his largest impediment to re-election.
And Mr Clinton, with his folksy grin and familiar Arkansas drawl, responded with an unhesitating and characteristically long-winded endorsement of Mr Obama.
"I want to nominate a man who is cool on the outside but who burns for America on the inside," he said.