(Reuters) - Democrats launch their case for Barack Obama's re-election at their party convention on Tuesday, looking to draw a sharp contrast with Republican Mitt Romney and convince voters that the U.S. president deserves four more years to fix the economy.
A speech by first lady Michelle Obama caps the opening night of the three-day gathering in Charlotte, North Carolina, which concludes with Obama's acceptance of the nomination in an address on Thursday in a 74,000-seat downtown football stadium.
The convention gives Obama a chance to recapture the political spotlight from Romney and Republicans, who used their gathering last week to repeatedly attack Obama's economic leadership.
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 unacceptable alternatives.
"The real issue now in the election is: who's got the best plan going forward?" Democratic Senate candidate Elizabeth Warren of Massachusetts, who speaks to the convention on Wednesday, said on ABC's "Good Morning America" program.
"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 percent unemployment rate.
Republicans also criticized Obama for telling a Colorado television reporter on Monday night that he would give himself a grade of "incomplete" for his first term.
'A PASSING GRADE?'
"If President Obama can't even give himself a passing grade, why would the American people give him another four years?" Romney campaign spokeswoman Amanda Henneberg said.
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" in polls 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 percent rated the speech as excellent or good; the previous worst had been Republican John McCain's in 2008, at 47 percent.
Democrats plan to use their convention to highlight the party's diversity, featuring a lineup 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 on Tuesday will be San Antonio Mayor Julian Castro, a Hispanic rising star in the party.
Michelle Obama's speech will counter 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 polls show have had a hard time warming up to the sometimes stiff former Massachusetts governor.
"I think the first lady plays a special role because she will have personal perspective on the president's leadership - his grit and determination during a challenging time for our nation," Obama campaign spokesman Ben LaBolt said.
"She is a character witness for the president and someone who can address how he has made decisions as the nation has confronted these challenges," he said.
While Republicans focused at their convention on attacking Obama and helping voters get to know Romney, Democrats have in some ways a more difficult task of keeping up voter enthusiasm for an incumbent in tough economic times.
They will spell out Obama's successes during his first term - from ordering the mission that killed al Qaeda leader Osama bin Laden to the bailout of the auto industry.
The opening session will convene at 5 p.m. EDT, and Democrats will approve their non-binding party platform, which includes calls for higher taxes on the wealthiest Americans and support for same-sex marriage and a woman's right to abortion.
Former President Jimmy Carter will be featured in a video on Tuesday. Former President Bill Clinton will highlight Wednesday's slate of speakers in an address that could remind voters of his Democratic-led economic growth in the 1990s while appealing to the white working-class Democrats that Obama has had difficulty winning over.
The Obama campaign also plans to use the convention and Obama's speech on Thursday as an organizing tool to help them in North Carolina, a battleground state that Obama won in 2008 but polls show is too close to call this time around.
Organizers were nervously watching the weather as scattered thunderstorms were predicted for Thursday night when Obama was due to give his speech in an open-air stadium.