I think it's a private matter, and I also don't really think it matters. They'll confess to any faith if they think it can get them votes.
Why not? If God has a problem with it I'm sure he'll let us know.
edit: Isn't the issue here not what the leader believes in but the impact of those stated beliefs upon his mission? It's not an issue of whether or not it's stupid or not for the political leader to believe certain things, right?