The religious faith of America's leaders often is of the utmost importance to their political success. President Barack Obama has used the fact that his father was a Muslim to foster better relations with the Islamic world. And analysts say that a recent public opinion poll showing that nearly 20 percent of people believe the president is a Muslim suggests that Americans are increasingly confused about the president's spirituality.
Visitors from around the country stop to take pictures in front of the White House. Trudy Lehnen of the Midwestern state of Illinois says she is unclear about President Obama's faith.
"I don't know what he is," she said. "But I don't think he's a Christian, and I do think he leans towards the Muslims.'"
She says that is because she feels that the president's foreign policy favors Muslim countries over traditional allies like Britain and Israel.
Her husband Tom agrees.
"I think the bottom line is you never truly walk away from your upbringing," he said.
The Lehnens' attitudes are in line with a public opinion poll by The Pew Forum on Religion & Public Life. Eighteen percent of those surveyed said they believe that President Obama is a Muslim, despite his self-identification as a Christian.
The study was conducted in late July and early August, before the president weighed in in the debate over a proposed Islamic cultural center near the site of the 2001 terrorist attacks on New York City.
Alan Cooperman, associate director for research at The Pew Forum, says the people who think Mr. Obama is a Muslim tend to be the same people who disapprove of his job performance, and that they might be trying send a message.
"I'm not even sure that all of those people genuinely think the president is a Muslim," he said. "Some of them are expressing the belief that he is a Muslim, partly perhaps as a way to say, 'He's not one of us. He's different.'"
Barack Obama's father was a Muslim. And although the president's critics used that against him during his election campaign, Mr. Obama said his heritage would help repair America's relations with the Islamic world.
Although the president identifies himself as a Christian, what many Americans remember is his association with the controversial preacher Jeremiah Wright, which became an issue during the campaign. And since taking office, President Obama has not publicized his attendance at church, like many of his predecessors.
The Pew Forum's Alan Cooperman says that might have allowed the president's most vehement critics to sow doubts about his religious devotion.
"A vacuum in the United States in the political arena tends to be filled," he said.
Even his supporters might be wondering. According to the Pew survey, only 46 percent of Democrats identify Mr. Obama as a Christian - down from 55 percent last year.
John Farina, a specialist on religion and society at George Mason University, says President Obama's Christian faith is different from the fervent, all-encompassing religiousness of many Americans, including African-American leaders like the late Martin Luther King, Jr.
"He is not your typical black politician when it comes to religion," he said.
The Pew survey shows that although African Americans are among the president's most ardent supporters, more than half are uncertain he is a Christian.
Mr. Obama is not the first U.S. president to deal with questions about his faith. John F. Kennedy's Catholicism was an issue during the 1960 campaign; he promised not to take instructions from the Pope.
But analysts say President Obama seems different. Faith is only one area of his life that critics attack. Another is his birthplace - some of the president's detractors question the veracity of Mr. Obama's Hawaiian birth certificate. The U.S. Constitution states that only natural-born citizens may be president.
"These kinds of [stories] - the dark conspiracy of history - thrive during periods of distress," said Fouad Ajami, who is at The Johns Hopkins University's Paul H. Nitze School of Advanced International Studies and Stanford University's Hoover Institution. "It's so in Europe in the middle ages; it's so in our own history; it's so in Islamic history - that once you have a people that are confused and who are in distress and in need economically and the time-honored ways are beginning to fail them and the assumptions are beginning to give way, that people believe anything."
Other reasons cited for the popularity of such beliefs about the president include the rise of the Internet and 24-hour, instantaneous news reporting. And experts point out that these beliefs come as President Obama's public approval ratings are at record lows.