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“Blue-collar whites did not back Obama in 2008, but this group turned even more fiercely against him since 2008 because of the economy and because they came to believe that Obama does not share their values or understand their lives,” Mr. Olsen said. “In 2010, Republicans carried non-college-educated whites by a 63-to-33 margin, a record high for a congressional election.”

In 2008, Mr. Obama lost whites without college education by a margin of 58 percent to 40 percent.

The challenge for presumptive Republican nominee Mitt Romney is to tap into that anger and persuade those voters to turn out again this year, said Ford O’Connell, who ran rural outreach for John McCain’s 2008 presidential campaign.

“This is the group that has soured on Obama the most. Therefore, Romney must appeal to white working-class voters and drive up their turnout or else he will lose in 2012,” he said. “If Romney fails to outperform McCain with white working-class voters, his only other path to victory is essentially to hope that Hispanics don’t turn out to support Obama, and frankly that is not a very good game plan.”

With four months until the election and the unemployment rate stuck at 8.2 percent, there are signs that Mr. Obama is struggling to re-create the same levels of support.

A Gallup poll release last month showed Mr. Obama’s support among all voters has dipped 5 percentage points since 2008 — and dropped slightly more among his key white constituencies, which include young adults and female college graduates.

Mr. Obama’s campaign is aware of the geographic challenges.

This week, it began running ads in Ohio and Pennsylvania highlighting the government’s bailout of General Motors Co. and Chrysler LLC. The campaign also is trying to undermine Mr. Romney’s message that his experience in the private sector has given him the skills needed to strengthen the nation’s economic recovery and get more people out of the unemployment lines.

“Mitt Romney’s companies were pioneers in outsourcing U.S. jobs to low-wage countries,” the ad says, citing news reports, which the Romney camp challenges, about Bain Capital investments in companies that moved jobs overseas. “He supports tax breaks for companies that ship jobs overseas. President Obama believes in insourcing.”

It’s a message Mr. Obama carried to Ohio on his bus tour Thursday, repeating the “pioneers” line to a cheering crowd.