Inside the arena, the convention hall cheered whenever Obama's image showed on the huge screen behind the speaker's podium, and roared when the late Sen. Edward M. Kennedy was shown mocking Romney in their 1994 Senate race.
"On the issue of choice, I am pro-choice, my opponent is multiple choice," the late senator said as crowd grew louder.
Romney supported abortion rights while serving as governor; he generally opposes them now.
Democrats unspooled insult after insult as they took their turn the week after the Republicans had their convention in Tampa, Fla.
Illinois Gov. Pat Quinn said that Republicans had omitted mention of Romney's term as Massachusetts governor at their gathering.
"We already knew this extremely conservative man takes some pretty liberal deductions. Evidently that includes writing off all four years he served as governor," Quinn declared.
Said Senate Majority Leader Harry Reid of Nevada, speaking of Romney: "Never in modern American history has a presidential candidate tried so hard to hide himself from the people he hopes to serve."
"When you look at the one tax return he has released, it's obvious why there's been only one. We learned that he pays a lower tax rate than middle-class families. We learned he chose Swiss bank accounts and Cayman Island tax shelters over American institutions."
In his campaign trip to Virginia earlier in the day, Obama told an audience at Norfolk State University that the economy will get worse if Romney wins the White House this fall and that Election Day apathy was his enemy — and theirs.
Republicans are "counting on you, maybe not to vote for Romney, but they're counting on you to feel discouraged," he said. "And they figure if you don't vote, then big oil will write our energy future, and insurance companies will write our health care plans, and politicians will dictate what a woman can or can't do when it comes to her own health."
On the final stop of a pre-convention campaign circuit of several battleground states, the president also dropped off a case of White House-brewed beer at a local fire station.
Romney was in Vermont as the Democratic convention began, preparing for three fall debates with Obama almost certain to be critical to the outcome of the election.
There was no shortage of political calculation behind the program of the convention's first night — or for any other. Polls show the first lady is more popular than her husband.
Democratic delegates bestow their nomination on Obama and Vice President Joe Biden on Wednesday night, when former President Bill Clinton delivers a prime-time speech aimed at voters disappointed with the results of the past four years yet undecided how to cast their ballots.
White men favor Romney over Obama in public and private polls, but a Gallup survey taken in July showed that 12 years after leaving office, Clinton was viewed favorably by 63 percent of the same group and unfavorably by only 32 percent.
Obama's acceptance speech caps the convention on Thursday night at the 74,000-seat Bank of America football stadium. Aides kept a wary eye on the weather in a city that has been hit in recent days with strong afternoon rains.
Republicans did their best to rain on Obama's convention, whatever the weather.
Vice presidential candidate Paul Ryan spoke in Westlake, Ohio, standing behind a lectern bearing a sign that read "Are you better off?"
Republicans released a web video that interspersed images of Obama and the economy's weak performance with slightly out-of-focus video clips of former President Jimmy Carter discussing the nation's economic woes when sat in the Oval Office more than 30 years ago.
Matthew Daly reported from Norfolk, Va. Associated Press writers Steve Peoples in Ohio, Kasie Hunt in Vermont, Jack Gillum and Tom Raum in Washington, Thomas Beaumont in Des Moines, Iowa, and Ken Thomas and Matt Michaels in Charlotte contributed.
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