Carson expressed a personal opinion. So what?
He doesn't appoint a President. The President is elected by the people. He can't remove ANYBODY from a presidential run, much less a Muslim candidate if one were to ever arise.
And by the way, look up the website of the Chaplaincy of the U.S. House of Representatives where you'll find the first daily opening prayer said in Congress, as well as years worth of daily opening prayers said in the House by Judeo-Christian clergymen.
I doubt you'll find a single prayer to Allah spoken by Muslim clergy there in the House. The God of Abraham, Isaac and Jacob has ALWAYS been The God in whom our nation trusts.
First Prayer of the Continental Congress, Office of the Chaplain