The new Pew poll on religion tells us two things. One: Mitt Romney's Mormonism, which hasn't broken out as an issue since Pastor Robert Jeffress blew it up, isn't hurting him. Two: Confirmation bias is keeping the "Obama's a Muslim" number nice and high.
It's rather easy to track the second trend. The moment at which the most people thought Obama was a Christian (he is, though, not a particularly churchy once since he left Jeremiah Wright's house) was right before the 2008 election. Fifty-five percent of people thought he was Christian; 12 percent said he was Muslim. After Obama became president, he became better-known -- and it did nothing to convince people he was Christian. That number plunged to 38 percent in the summer of 2010, when Obama was unpopular. It's back up to 49 percent now, as Obama's recovered some support. Theories of the president's religion are reliant on his policies.
That explains the figure I clipped at the top of the post. Most of the growth in Obama-Muslim theorizing has occured among Republicans. One in six of them used to think Obama was Muslim; one in three of them now do. There's no follow-up, but you can count off the things that conservative Republicans haven't liked about Obama. The Cairo speech. "Apologizing for America." Wanting to close Gitmo. Afghanistan timetable. Siding with rebels in the "Arab Spring," and watching the Muslim Brotherhood take the lead from the rebels in classic Bolshevik/Menshevik tradition. Then, most recently, you've got theories about the Muslim Brotherhood infilitrating the government. The people who don't like Obama start with policy, then make assumptions about religion.