I wouldn't go that far to say he did this to offend Christians. I think he just really likes POTUS. And no he probably wouldn't intentionally offend Muslims. Very few people would these days. I don't aim to to offend anyone intentionally, but if their feelings get hurt, like many Christians with his painting, that is a result of his actions. I will leave it at that. I think the painting is stupid, regardless of who it would have been.
If you really like a politician, you can paint him in a thousand other ways. If you choose a universally known religious symbol to equate your politician with a deity people actually worship, you are being blasphemous. The difference is that today's Christian's won't imprison or execute you for blasphemy, but today's Muslims will take out as many of your citizenry as they can.