Mrs. Obama is expected to make the case that Obama is the best candidate to advocate on behalf of the middle class because he has experienced their struggles himself.
Many voters already have heard Mrs. Obama's stories about her husband being raised by a single mother and his grandparents or having struggled to pay off student loans.
But she is emphasizing them again in this campaign in hopes of drawing a contrast with Romney's privileged upbringing.
Polls show voters think Obama understands the economic issues that are important to them better than Romney, even though the Republican has an edge on who voters believe is better suited to manage the economy.
Former President Bill Clinton, who is emerging as one of the campaign's most effective surrogates, will headline the convention Wednesday and formally nominate Obama. He hopes to remind voters of the flush economy he presided over and make the case that Obama's policies will lead to similar results.
Vice President Joe Biden and Massachusetts Sen. John Kerry will address the large stadium crowd Thursday night before Obama speaks.
Kerry, seen as a potential second-term secretary of state under Obama, will try to capitalize on the Democratic Party's rare advantage on national security issues. He is expected to trumpet Obama's decision to order the raid that killed Osama bin Laden and the president's plan to end the Afghanistan war, a sharp contrast to Republicans who rarely mentioned the war during their convention or the tens of thousands of troops still engaged in combat.
Obama's young daughters start school in Washington next week and are not expected to have a formal role at the gathering. But they could come to Charlotte Thursday night for their father's acceptance speech.
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