He endorsed Mitt Romney four years ago -- but now, Donald Trump is describing the 2012 Republican nominee as a "stiff" who "didn't know what he was doing" when he lost the election to Barack Obama.

Trump's comments on NBC's "Today" show are a response, ahead of time, to a speech Romney is delivering today in Utah. According to excerpts of the speech, Romney will brand Trump as a "phony" and "fraud" whose "promises are as worthless as a degree from Trump University."

Mitt Romney says prospect for safe future 'greatly diminished' if Trump becomes GOP nominee.

Romney isn't expected to use the speech to endorse a rival to Trump.