VIDEO-----> Mitt Romney Goes On Jimmy Kimmel To Trash Trump

Is he just a guest on late night? No. It's clear when Mitt Romney first sits down that he's there to tell the world why Trump must be stopped. The audience cheers.

He calls Trump a "phony" and goes after him on his tax returns. Again, he doesn't mention defeating Hillary Clinton, not once,  just Trump.

Watch: Romney goes after Donald Trump within 30 seconds of taking the seat.