CHARLOTTE, N.C. — Democrats open their national convention Tuesday in defense of a president who carries both the power and the burden of incumbency, offering President Barack Obama as the best choice to revive the ragged U.S. economy and asking Americans to be patient with incomplete results so far.

Michelle Obama's evening speech will be an early highlight of a three-day schedule that has drawn thousands of delegates to a state Obama narrowly carried in 2008. Although Obama no longer is the fresh-faced newbie who leveraged a short Senate career into an audacious run for the nation's highest office, he still can excite partisans, and Democrats were counting on massive numbers to pack a stadium for his speech later in the week.

The Democrats dispatched U.S. Senate candidate Elizabeth Warren, who hopes to unseat Republican Scott Brown in Massachusetts, to make the case for Obama on morning talk shows, and she acknowledged that "it's tough out there" for many Americans. But she insisted that Obama offers the better vision going forward.