Clinton's prime time speaking slot at the convention, like his central role in the Obama ad airing in key states, is seen as an effort to narrow Romney's advantage with these voters, who could tip the balance in a close election.
"Bill Clinton has very favorable approval numbers," said Katon Dawson, a national political consultant and former South Carolina Republican Party chairman. "He's a pretty tough adversary for us."
AP Special Correspondent David Espo in Charlotte, N.C., contributed to this report.
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