Democrats launched their case for Barack Obama’s re-election at their party convention yesterday, seeking to draw a sharp contrast with Republican Mitt Romney and convince voters that the US President deserves four more years to fix the economy.

Convention will highlight the party’s diversity

A speech by First Lady Michelle Obama capped the opening night of the three-day gathering in Charlotte, North Carolina, which concludes with Obama’s acceptance of the nomination in an address tomorrow in a 74,000-seat downtown football stadium.

The convention gives Obama a chance to recapture the political spotlight from Romney and the Republicans, who used their gathering last week to repeatedly attack his economic leadership in his first term.

The task for Obama and his allies will be to persuade voters disappointed by his first White House term that things will be better the second time around, while portraying the budget-slashing economic remedies offered by Romney and his running mate, congressman Paul Ryan, as really being unacceptable alternatives.

“The real issue now in the election is to determine who’s got the best plan going forward,” Democratic Senate candidate Elizabeth Warren of Massachusetts, who speaks to the convention today, said on ABC’s Good Morning America programme.

“Mitt Romney has made clear what his plan is: cut taxes for the richest Americans and the biggest corporations, increase taxes on the middle class and don’t make any investments in the future.

“Barack Obama says that’s not the right way to do it,” she said.

Ryan and Republicans kept the pressure on Democrats with a question they highlighted after their convention last week: Are voters better off after nearly four years of Obama?

“We’re not better off than we were four years ago. Look at all the statistics,” Ryan said on Good Morning America, citing the slow economic recovery and 8.3 per cent unemployment rate.

Republicans also criticised Obama for having told a Colorado television reporter on Monday night that he would give himself a grade of “incomplete” for his first term.

“If President Obama can’t even give himself a passing grade, why would the American people give him another four years?” Romney campaign spokesperson Amanda Henneberg asked.

Romney and Obama are running close in opinion polls ahead of the November 6 election, but Obama hopes to get more of a convention “bounce” than Romney, who gained a few percentage points at most from the Tampa, Florida, event.

A Gallup poll on Monday showed Romney’s speech last week got the worst scores of any convention acceptance address going back to 1996, when it began measuring them. Thirty-eight per cent rated the speech as excellent or good; the previous worst had been Republican John McCain’s in 2008, at 47 per cent.

Democrats plan to use their convention to highlight the party’s diversity, featuring a line-up of black, Hispanic and young speakers to appeal to the voting blocs that helped propel Obama to a comfortable victory in 2008.

The keynote speaker last night was San Antonio Mayor Julian Castro, a Hispanic rising star in the party.

Michelle Obama’s speech aimed at countering a successful Republican convention appearance last week by Romney’s wife, Ann, who helped present a softer and more personal side of Romney to voters, who have had a hard time warming up to the sometimes stiff former Massachusetts governor, polls show.

Former President Jimmy Carter also featured in a video last night and former President Bill Clinton will highlight today’s slate of speakers in an address that could remind voters of his Demo-cratic-led economic growth in the 1990s while appealing to the white working-class Democrats whom Obama has had difficulty winning over.

The Obama campaign also plans to use the convention and Obama’s speech tomorrow as an organising tool to help them in North Carolina, a battleground state that he won in 2008 but polls show is too close to call.

Organisers were nervously watching the weather as scattered thunderstorms were predicted for tomorrow night, when Obama is set to give his speech in an open-air stadium.