Yes he is, and so is Dan Rather. Except Rather is not President right now, Trump is.
I don't know if I would call Rather a compulsive liar so much as a victim of his own bias. He so desperately wanted something to be true than no red flag was going to stop him from reporting it.
Trump lies for no apparent reason and seems to be getting worse because people are allowing it. He told Wolf Blitzer that he didn't actually believe the story about Rafael Cruz and JFK but he said it anyway because he wanted to win. He then returned to telling the lie within days.
The worst part is the so called religious leaders who apparently think they're hiding in God's blind spot and think it was fine to promote and encourage such a clearly immoral man.