With exactly a year remaining until American voters determine if Barack Obama deserves a second term, a new poll shows cause for worry at the White House – independents, in particular, have lost faith in the Democratic president. Moreover, Mr. Obama’s performance scores as many failing grades as it does soaring marks from the general public.

Thirty-five percent of independents, the critical mass of voters with the power to swing presidential elections, say Obama deserves to be reelected, while 56 percent believe he does not, according to a Christian Science Monitor/TIPP poll released Monday. Ten percent are not sure or did not say.

Among Americans of all political persuasions, 40 percent of those polled would give Obama four more years, 50 percent would not, 6 percent were not sure, and 4 percent declined to answer.

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“The independent support is key. They are a key voting bloc to get him reelected,” says Raghavan Mayur, president of TechnoMetrica Market Intelligence, which conducted the poll of 901 Americans. “When your support is weak among independents, it really is concerning.”

If history is any guide, however, Obama’s current approval ratings will be an unreliable predictor of his fate in the November 2012 contest. With the Republican nomination race in full swing and early-state primary elections just two months away, the GOP’s lack of consensus around or enthusiasm for a particular candidate could play in Obama’s favor.

“Obama should indeed be worried, but so should the Republicans,” says H.W. Brands, a professor of history at the University of Texas at Austin. “If the Republicans could rally behind a centrist candidate, one who could attract the moderate voters that swing general elections, the dismal economy would doom Obama. But the Republicans appear to have been taken captive by their right wing, which wins primaries but scares general-election voters. So at the moment I'd call it a toss-up.”

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Gallup’s historical data indicate that Obama’s approval ratings, while grim, are not without precedent for reelection.

In the 10th quarter of his presidency (between April 20 and July 19, 2011), Obama’s job approval average, at 46.8 percent, was sub-50 percent, the threshold that pundits and journalists use to gauge a leader’s appeal in the run-up to an election. But Bill Clinton and Ronald Reagan also rated below that marker during the same period of their respective first terms. President Clinton was at 49.3 percent, and President Reagan scored a meager 44.4 percent. Both, of course, went on to reelection.

Jimmy Carter’s 31 percent ranking during the 10th quarter of his tenure was too low to overcome. And, by contrast, George H.W. Bush’s enviable 73.6 percent didn’t spell success in the 1992 contest.

Gallup’s quarterly averages don’t date back to Harry Truman’s day, but Gallup polling six months before Truman's reelection shows just 36 percent of voters had a favorable view of the Missourian’s performance in office, and 50 percent disapproved. There were similarities between the circumstances facing Obama and those Truman tackled, namely stagnating economies and midterm congressional losses to the GOP.

“Harry Truman is the likeliest historical parallel, although Truman's economic troubles weren't as difficult as Obama's,” Mr. Brands says. “But he blamed the 'do-nothing Congress' for playing party politics while the nation's interest languished. And he squeaked to reelection. Obama seems to be following Truman's lead.”

In the Monitor/TIPP poll, 37 percent of those surveyed rated Obama’s overall performance an A or B. But 38 percent give him a D or F. One-quarter graded Obama, the former president of the Harvard Law Review whose message of hope and change galvanized a historic coalition of young voters and minorities in 2008, as average, bestowing a C grade.

The survey, administered from Oct. 31 to Nov. 6, has a margin of error of plus or minus 3.3 percentage points.

Underlying the dissatisfaction is grave voter anxiety about the economy, says Mr. Mayur – and the government’s job statistics don’t tell the full story. The Monitor/TIPP poll shows that up to 25 percent of US households include at least one individual looking for full-time employment, he says.

“There is a lot of underemployment, and that’s why we right now believe that the true job situation is not being reflected” in government numbers showing unemployment at 9 percent in October. “The pain is much worse than that,” says Mayur.

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