UFC's Colby Covington and Kamaru Usman Go Nuclear, Trump Calls In

If you think the Presidential election has gotten ugly, check out the intensely angry exchange between 2 UFC fighters ... and Donald Trump makes it clear whose side he's on.

Colby Covington had just defeated Tyron Woodley Saturday night when he appeared on the post-show with his arch-enemy ... Champion Kamaru Usman, who defeated Covington last December for the title. Covington, who was enraged the fight was stopped, is demanding a rematch.

And, that's the backdrop for some trash talking ... the likes of which you haven't heard in a while. The 2 men are talking at the same time ... Covington threatening Usman -- "When I see you, you're dead" -- while Usman laughs it off, claiming he broke Covington's face when they fought.

Covington invokes Trump's name, saying, "I got the President of the United States, dragon energy." And, soon after that, Trump called Covington to congratulate him on beating Woodley. Trump says, "I just made a big speech to 35,000 people and said, 'Oh, I've got to get home now and watch Colby.'"