As with the deeply conservative Republican platform, not all of which Romney endorses, nothing binds Obama to the specifics of the party's manifesto.
The president rallies in Virginia on Tuesday before joining the convention a day later.
Michelle Obama said she wants to use her opening speech to "remind people about the values that drive my husband to do what he has done and what he is going to do for the next four years. I am going to take folks back to the man he was before he was president."
San Antonio Mayor Julian Castro delivers the convention's keynote address Tuesday night, a nod to the importance of Hispanic voters in the race.
"Under any score — immigration, education, health care — in any number of issues, he has been a very effective advocate for the Latino community," Castro said of Obama during an interview on CNN.
With flourishes but no suspense, Democrats will march through the roll call of states renominating Obama for president and Joe Biden for vice president on Wednesday.
That's also when the convention hears from Bill Clinton, whose 1990s presidency is being trumpeted by Democrats as the last great period of economic growth and balanced budgets — a further redemption of sorts, at least from his party, for a leader who survived impeachment over sexual scandal.
Obama's big acceptance speech is Thursday, and Democrats are closely monitoring the weather forecast since he's scheduled to speak outdoors at Bank of America stadium.
Obama campaign manager Jim Messina said Tuesday during a panel discussion with ABC News and Yahoo! News that the president's speech would be held outdoors "rain or shine" — unless the weather would put people at risk.
Heavy evening rains doused Charlotte over the Labor Day weekend. Thursday's forecast calls for a chance of rain.
The Democrats were working to leverage the impact of the convention with events around the country. Obama, in an email to supporters, said actor Kal Penn — who worked in Obama's White House — would host a special online program before Thursday night's convention speech featuring special guests and interviews with Mrs. Obama and Biden.
As part of that effort to reach beyond the convention hall, the first lady will present the Top 10 List on David Letterman's show Wednesday night.
Obama came out with a campaign commercial asserting that, under Romney, "a middle-class family will pay an average of up to $2,000 more a year in taxes, while at the same time giving multimillionaires like himself a $250,000 tax cut." Aides said it would be seen in Colorado, Iowa, New Hampshire, Nevada, Ohio and Virginia, the battleground states where the White House race is likely to be decided.
The president and aides have acknowledged for weeks that they and the groups supporting them are likely to be outspent by Romney, and recent figures say that has been the case in television advertising in the battleground states for much of the past two months.
Democrats chose North Carolina for their convention to demonstrate their determination to contest it in the fall campaign. Obama carried North Carolina by 14,000 votes in 2008, but faces a tough challenge this time given statewide unemployment of 9.6 percent, higher than the vexing national rate of 8.3 percent.
Woodward reported from Washington. Associated Press writers Ben Feller in LaPlace, La., Philip Elliott in Detroit, Kasie Hunt in Wolfeboro, N.H., and Ken Thomas, Michael Biesecker, Mitch Weiss and Beth Fouhy in North Carolina contributed to this report.
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