Of course, the American experiment was founded on Protestant Christian ethics and values. It was also designed to safeguard the rights of dissidents. It is foolish to suggest that a Jew or Moslem could not be elected. All they need are votes. At one time, it seemed inconceivable that there could be a Roman Catholic president, now it seems, not unlikely, that the most electable candidate in the Democratic Party is African-American. The Democrats nominated a Jew for Vice President. A Moslem, in today's climate, is a long shot but that would not be because he wasn't a Christian.
Is it an advantage to be Christian in the US? Not nearly as much as it once was. We live in an era of cycicism and suspicion toward old values. In the glare of factual enlightenment, in the revelation of clerical misconduct, our society has, to an extent, eschewed Christian context while trying to retain Christian ethics. The resultant chaos from "God is dead" to " Love thy neighbor, anyway".
Ours is an open society, with all the pluses and minuses that brings. And, it is a society with a proud history. Our founders were the guys who said no kings, no aristocracy, no supression of the press, everybody gets a vote (ok, it took them a while to get around to that), everybody gets a jury trial and lots more good stuff. Now, there are always going to be clowns, like we are dealing with now, who try to screw with the system but, try as they might, it's still there. It cleanses itself.