Seth Lipsky, who has written an indispensable book on the Constitution, notes that the President's religion should be considered perhaps the most inappropriate subject of all for partisan political discussion:
":..(W)hat we haven't seen -- or, more importantly, heard from the president -- is reference to the constitutional point. The one qualification for public office under the United States that was flatly outlawed by the Founders of our country is a religious test. It is prohibited in main body of the Constitution, in Article VI. It requires that all senators and representatives, and all members of all the state legislatures, and all executive and judicial officers -- both of the federal and state governments -- must be bound over by an oath or affirmation to support the Constitution of the United States. Then it lays down the famous prohibition: ". . . no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States."
Read the whole thing.