President Barack Obama has declared himself a Christian. He has worshipped in Christian churches, prayed with Christian ministers, and recounted how he knelt beneath a cross and felt God's spirit. And yet, a surprising number of Americans keep telling pollsters they believe he's a Muslim. The Pew Research Center last week reported that 18 percent of Americans believe Obama is a Muslim, up from 11 percent in March 2009. A Time magazine poll also released last week found even more -- 24 percent -- said he was a Muslim.