“But then this nonsense about ‘Oh, how did he get into Harvard, how did he get into Columbia, I’d like to see his grades from Occidental, how was he able to write such a memoir?'” Letterman said, paraphrasing Trump’s criticism of Obama’s educational record, the strangely chosen issue that the real estate magnate moved to after Obama produced his long-form birth certificate. “That’s taking on a whole different point of view as far as I’m concerned… Other people are not amused by this tactic. And by the way, nobody should be amused by that.”

After guest Dr. Phil’s lukewarm defense of Trump, Letterman continued his verbal assault on Trump’s integrity.

“My point is it’s all fun, it’s all circus, it’s all a rodeo, until it starts to smack of racism,” he said. “And then it’s no longer fun… I have heard enough really smart people to convince me that yes, that is very, very insulting… How can you say things like that if you’re not a racist?”

Letterman would go on to say that if Trump did come on his show — and he was unsure if he even wanted him to do so — he would be expecting an apology from Trump for his behavior.

The harsh words didn’t sit quite well with Trump, who was also smacked around at the White House Correspondents dinner by both President Obama and host Seth Meyers. According to the NY Post, which seems to be Trump’s personal courier, the maybe-candidate fired off a letter to the CBS late night host to both defend himself and hit back as best he could.