Tens of thousands of people who together gave millions of dollars to Barack Obama's 2008 presidential campaign have gone missing this time around. Their failure to give so far may signal that some of the president's earliest supporters have lost enthusiasm.

At the same time, Republican rivals like former Massachusetts Gov. Mitt Romney have been gaining financial strength in parts of the country that were instrumental in swinging the last election for Obama, according to an Associated Press analysis of new campaign finance data.

The president's re-election effort is hardly hurting for cash: His campaign and the Democratic Party raised more than $70 million combined since July, outstripping all Republicans combined by millions. But some supporters who wrote Obama larger checks early in the 2008 campaign haven't done so this time, representing more than $10 million in missing donations.

The AP's analysis suggests that Obama, beleaguered by a struggling economy, will have to work harder to win back party stalwarts and swing voters alike. His approval ratings have slumped to 41 percent in a recent Gallup poll, as steadfast supporters have found themselves less able or less willing to open their wallets again.

"He was our state senator, and when I looked at the Republican side, I thought, `We need some fresh blood in the campaign,'" said Janet Tavakoli, 58, a financial analyst from Chicago who gave $1,000 to Obama in 2008. "But I was dead wrong about it," she said, and isn't supporting any candidate this time.

Obama is running unchallenged this primary season, so potential donors might not feel a sense of urgency. But early donors tend to give again, and larger donations are the strongest signs of enthusiasm _ something Obama enjoyed four years ago _ as Romney picked up cash in swing states.

Obama also missed support from early donors from places in Illinois, Michigan and Texas he narrowly won in 2008. At the same time, Romney raised more than $1 million from those same areas, mostly from Houston donors; he also gained support from solid-leaning Obama districts in Southern California, Florida and New England. Overall, Obama lost Texas but handily won Michigan and Illinois.

"I have little discretionary money, and I just have to take care of myself," said Roger Hodges, 45, an urban designer in Richmond, Calif. Hodges gave Obama $250 four years ago but doesn't plan on donating in this election, adding that his friends in the liberal-leaning San Francisco Bay Area have become disappointed with Obama.

The Obama campaign said almost all of its donors this year have given $200 or less. Yet nearly 40 percent of Obama's fundraising coffers since April have been filled with donations larger than that, compared with 76 percent during the same period four years ago when Obama faced Hillary Rodham Clinton for the Democratic nomination.

For its analysis, the AP compared the names and addresses of Obama contributors who gave between $200 and $2,500 from April to September 2007 with those who gave amounts in the same range during the same period this year. The AP adjusted its analysis to compensate for contributors who might have moved or listed a slightly different name.

Records also show a handful of Obama contributors from 2008 donated to Romney this time; none appeared to give to Texas Gov. Rick Perry, another leading GOP candidate.

Lynda Marren, 48, of Hillsdale, Calif., usually supports Republican politicians, but she paid $500 to hear Obama speak four years ago. "I wasn't persuaded then, and still am not," she said, and gave $1,000 to Romney last June.

Many Obama supporters said they will vote for his re-election even if they don't write big checks. About 4 out of 5 of those who voted for the president in 2008 say they are likely to do so again, according to a new NBC News/Wall Street Journal poll.

But Obama's contributions this recent fundraising quarter _ absent support from the Democratic National Committee _ are less than the combined cash given to all GOP candidates, hinting at an influx of money to whomever Republicans chose as their nominee. Observers have said this election likely will cost more than $1 billion.

The Obama campaign, for its part, said more than a million people have given to the president's 2012 re-election efforts, a mix of hundreds of thousands of new and returning donors that spokesman Ben LaBolt said points to "evidence of a growing organization." All told, Obama received donations from a wide swath of the United States from the Plains, the Midwest and parts of the South since April, the AP's analysis found.

Among those donors was Laurel Cappa of Washington, who gave $300 to the president four years ago and opened her wallet again this year.

"It was a birthday gift to myself," she said, having turned 70 this year, "and I expect to be giving more."

The campaign reports offer a complicated financial picture for Obama this election cycle. Recent reports show a mixed level of financial support from Wall Street, and an AP analysis earlier this month found Obama garnered continued donations from the nation's most economically hard-hit areas.

The campaign figures, however, didn't capture money raised by new, outside groups known as super political action committees, which can collect unlimited amounts of cash to influence elections. Obama and leading GOP candidates all have super PACs working in their favor, not counting groups like the GOP-leaning American Crossroads that have raised hundreds of millions ahead of the general election.

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