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President Obama began a 10 day family vacation on Martha's Vineyard confronted by poll numbers reflecting an increasing belief that Mr. Obama, a self-proclaimed Christian, is a Muslim.

Two national surveys, one taken before and one taken after the president spoke out about plans to build an Islamic center and mosque near Ground Zero, reveal what pollsters call an unprecedented rise in misimpressions about a president's faith.

"I haven't seen any example, and I've been following polling of presidents for a long time now, of where we've seen increased confusion about religiosity the longer they're in office," says John Green. University of Akron politics professor and Senior Fellow with the Pew Forum on Religion and Public Life.

The Pew Forum found 18 percent of Americans now believe the president to be a Muslim, up from 11 percent a year ago. The percentage who believe Mr. Obama to be a Christian fell from 48 percent to 34 percent.

While Mr. Obama's political opponents are more likely to believe he's a Muslim, uncertainty has seeped into the president's political base.

"Now less than half of Democrats say the president is a Christian," Alan Cooperman of the Pew Forum says. "[L]ess than half of African Americans say the president is a Christian. Less than half of people who give Obama a positive job approval rating say he is a Christian."

In Washington, of the twelve people who talked to our Fox news crew, eight called the president a Christian, three were unsure, and one labeled him a Muslim.

Rodney Hawkins of Dallas, Texas said, "There is no doubt about it, he's Christian."

Another man told us, "There's no practical demonstration of the fact that he's anything other than Christian."

But one woman said, "The American public would like to know where he does stand on his faith."

A Time magazine poll, taken after the Ground Zero mosque debate flared, found 47 percent believe the president is a Christian but 24 percent believe, again incorrectly, that he's a Muslim.

The president has attended Christian services sparingly and given up on a vow to find a permanent church in Washington; this, after a campaign season decision to quit his Chicago church and sever ties to long-time pastor, Jeremiah Wright. Mr. Obama now prefers private Christian services at Camp David. Also, Mr. Obama plays a lot of golf on Sundays.

Still, scholars find these poll numbers baffling.

"It just seems ridiculous to me that he would be considered a Muslim by anyone," said Charles Camosy, a theologian professor at Fordham University. "I mean we are in the middle of Ramadan now where Muslims are fasting from dawn to dusk and we have our president stuffing his face with ice cream." The first family stopped for some ice cream while relaxing in Florida last weekend.

In addition to this visual evidence, the White House says Mr. Obama receives an e-mailed prayer devotional each day. He also prays each day.

Aides say, however, the president does not wear his faith on his sleeve; something pollsters say may be part of the problem. Deputy White House Press Secretary Bill Burton explained, "The president's top priority here isn't making sure that Americans know what a devout Christian he is."