Bloomberg is an ideological centrist in a way that now seems almost quaint, and his endorsement of Clinton on Wednesday night was more an anti-endorsement of Trump. He hammered Trump, questioning his actual wealth, calling him a con man and a hypocrite, and suggesting that Clinton deserved votes because she is "sane" and "mature."
And on Thursday, as Clinton was preparing to accept her party's nomination, Trump got mad about it.
At an event in Iowa, he started talking about how he wanted to "hit" the Democratic speakers at the convention who were disparaging him. The choice of words was awkward, but it seems clear he meant it in the way he's used it throughout his campaign: To go after them with verbal or tweeted insults.
"I was going to hit one guy in particular, a very little guy," Trump said, making a clear reference to Bloomberg's stature. "I was going to hit this guy so hard his head would spin and he wouldn't know what the hell happened. He came out of nowhere!"
Trump continued to assail Bloomberg on Twitter on Friday morning, starting off with another joke about his height.
As BuzzFeed's Andrew Kaczynski pointed out on Twitter, Trump's attitude on Bloomberg's final term has changed pretty substantially of late. Here's Trump tweeting about Bloomberg during the latter's final term.
And shortly before he left office.
And, of course, praising Bloomberg for giving him a project.
All of Trump's tweets above came before Bloomberg denounced him on television. As we've seen so many times in the past, nothing changes Trump's opinion on someone faster than their expressing a negative opinion of him.
Update: ...but a former Bloomberg spokesman did.