Trump told Bill O'Reilly: "You've always been fair to me, Bill. I've never had a problem with you. You've always treated me with respect and fairly."
The host then warned the billionaire: "Well, that's gonna change tonight."
O'Reilly asked Trump about the shot he took at Republican rival Marco Rubio that received boos last week. He told a crowd that Rubio is "a clown."
Trump walked back the comment Tuesday night – kind of.
O'Reilly told Trump: "Calling him a 'clown,' that's not presidential."
Trump seemed to get upset and said: "Okay listen, okay, excuse me Bill. He was a member of the 'gang of eight,' which was a disaster, he was totally weak on immigration and, by the way, he hasn't changed."
"That's fine; it's the 'clown' stuff that's not fine. Last question," said the host.
"Well, okay, I can understand that," said Trump.
And it's another day another feud. Trump is now on the warpath with Forbes magazine -- which just unveiled its annual list of the 400 wealthiest Americans.
Forbes says Trump's net worth is $4.5 billion not the $10 billion-plus he claims.
But Trump is firing back, telling the magazine: "Look, all I can say is Forbes is a bankrupt magazine, doesn't know what they're talking about. It's embarrassing to me."
Trump is also on the cover of the new People magazine -- along with wife Melania and his youngest child, nine-year-old Barron.
In her first major interview since Trump declared he was going to run for president, Melania says she's optimistic that her husband can win.
She told the magazine: "It's a long road. I take it day by day. My husband has a lot of people cheering for him. We will see."
Former President Bill Clinton is speaking out about Trump's take-no-prisoners style. He told CNN: "You can't insult your way to the presidency."
Watch Below: Does Melania Trump Have What It Takes to be the Next First Lady?