Democrats turned Wednesday 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 Obama is steering the country to an economic recovery.

Clinton, in a rousing address to a television audience of millions, conceded that many struggling in a slow-recovery economy don't yet feel improvement, but said circumstances are indeed getting better, "and if you'll renew the president's contract you will feel it."

Clinton formally nominated Obama as the Democratic candidate in what is expected to be a tight race against Republican Mitt Romney. Minutes later, delegates at the Democratic National Convention in Charlotte, N.C., began the state-by-state roll call vote to make the nomination official.

Obama's acceptance speech Thursday will mark the climax of the convention, though Democrats have abandoned plans for 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 Obama's devotion to big-government solutions has stifled the U.S. economy and swollen the national deficit. Democrats have countered that Romney would go back to the economic policies that led to a recession, helping the wealthy while harming the poor and middle class.

Clinton followed through on the theme.

"If you want a you're-on-your-own, winner-take-all society, you should support the Republican ticket," 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."

Clinton described the Republican campaign argument as fairly straightforward. "It went something like this: We left him a total mess. He hasn’t cleaned it up fast enough. So fire him and put us back in."' He said Obama has 'laid the foundation for a more modern, more well-balanced economy.'

After the speech, Clinton was joined onstage by Obama, who made his first appearance at the convention. The former president bowed, and Obama pulled him into an embrace as thousands of delegates jammed into the convention hall roared their approval.

Populist charm

Clinton was a striking choice for one of the convention's prime speaking slots. He's had a checkered relationship with Obama, who ran against Clinton's wife, Hillary, in the 2008 primaries. The styles of the presidents are opposites: Clinton is outgoing, emotional and chatty, while Obama is cool, meticulous and reserved.

Whatever the differences between presidents current and past, Obama and his top aides looked to Clinton as the man best able to vouch for him when it comes to the economy, his largest impediment to re-election.

And Clinton, with his folksy grin and familiar Arkansas drawl, responded with an unhesitating and characteristically long-winded endorsement of Obama.

"I want to nominate a man who is cool on the outside but who burns for America on the inside," he said.

Few American politicians are more popular than Clinton. Even Republicans, who tried to force Clinton from office on charges he lied under oath about an affair, try to draw a contrast with Obama by praising Clinton's record balancing budgets and reforming welfare. Opinion polls show Clinton is especially well-regarded among white male voters, a group that favours Romney.

The personal tensions between Obama and Clinton have eased with Hillary Clinton serving as Obama's loyal secretary of state — and a potential presidential candidate in 2016. Hillary Clinton is on an 11-day tour of the Asia-Pacific region and was in East Timor as her husband spoke.

Democratic platform criticized

Clinton's speech followed a boisterous first day of the convention in which Democrats painted Romney, a wealthy businessman and former Massachusetts governor, as a privileged millionaire who doesn't understand the struggles of regular Americans. Michelle Obama was the star speaker, talking about her husband's humble roots and speaking of his compassion.

The Democratic convention, like the Republican one in Tampa, was carefully crafted to avoid controversies. Still Democrats came under fire Tuesday for adopting a platform, a nonbinding declaration of principles and positions, that had no mention of God and no reference to Jerusalem being the capital of Israel. Though the Jerusalem reference is offensive to many Arabs who see the city as part of a future Palestinian state, both parties have long included it in their platforms as a sign of their unwavering support for Israel.

On Wednesday, embarrassed Democrats amended the platform to include references to God and Jerusalem as the Israeli capital. Some delegates objected loudly, but Los Angeles Mayor Antonio Villaraigosa ruled them outvoted. Campaign officials say Obama personally intervened to make the change.

Despite the dispute, the often-fractious Democrats have generally maintained unity as they try to regenerate the excitement that surrounded Obama's candidacy four years ago, when his inspirational message of hope and change led to his election as America's first black president. But after almost four years of bitter partisan battles and unemployment hovering at 8.3 per cent, Obama's support has dropped.

While polls show he is more widely liked than Romney on a personal level, Romney is seen as a better bet for improving the economy.

Romney framed the economic debate against Obama in an email to supporters Wednesday, writing that "no president in modern history has ever asked to be re-elected with this many Americans out of work."

In an interview on Fox News Channel, Romney said: "Anyone who wants him to try again will be making a big mistake."