President Trump mocked "The Tonight Show" host Jimmy Fallon on Twitter Sunday after the comedian expressed regret over how he handled a guest appearance by then-candidate Trump in September 2016.

The president said that Fallon is "whimpering to all that he did the famous 'hair show' with me (where he seriously messed up my hair), & that he would have now done it differently because it is said to have 'humanized' me-he is taking heat."

Trump also claimed that Fallon had called him after the Sept. 15, 2016 episode and said it had done "monster ratings," before concluding, "Be a man Jimmy!"

Fallon responded late Sunday in a tweet: "In honor of the President’s tweet I’ll be making a donation to RAICIES in his name." Fallon appeared to be referring to RAICES, the non-profit Refugee and Immigrant Center for Education and Legal Services.

Trump's opponents bashed Fallon for what they called a softball interview during which the former "Saturday Night Live" star playfully stroked the Republican nominee's hair. Fallon's NBC show eventually lost more than one-fifth of its audience and its late-night crown to Stephen Colbert's more liberal "The Late Show" on CBS -- a change that analysts have pegged to the political tides.

Fallon told a Hollywood Reporter podcast last week that he "made a mistake" in how he handled Trump's appearance, but denied that he supported the candidate: "I did not do it to 'normalize' him or to say I believe in his political beliefs or any of that stuff."

Discussing the backlash to the episode, Fallon said: "It's tough for morale. You go, 'Alright, we get it. I heard you. You made me feel bad. So now what? Are you happy? I'm depressed. Do you want to push me more? What do you want me to do? You want me to kill myself? What would make you happy? Get over it.'"

The host also decred what he called a "gang mentality" to the criticism.

"People just jump on the train, and some people don't even want to hear anything else. They're like, 'No, you did that!' You go, 'Well, just calm down and just look at the whole thing and actually see my body of work.'"

Fox News' Mike Arroyo and The Associated Press contributed to this report.