Sen. Al Franken (D-Minn.) said Friday night that his Republican Senate colleagues privately express “great concern” about President Trump's temperament, and he joked about the GOP eventually impeaching Trump.

Appearing on “Real Time with Bill Maher,” Maher asked Franken what Republicans really say behind closed doors.

Franken joked: “Well, there's a range in what they'll say, and some will say that he's not right mentally. And some are harsher.”

“No, no. That's not fair. That was cheap,” he continued. “There are some who I guess don't talk to me.”

Franken then got a bit more serious.

“I haven't heard a lot of good things, and I've heard great concern about the president's temperament,” he said.

Maher responded: “That's very diplomatic of you.”

To which Franken said with a smile: “Not very, was it? I don't think this was diplomatic, but I'll take it.”

Franken isn't the first Democrat to say Republicans senators are privately fretting. Sen. Sherrod Brown (D-Ohio) has said his GOP colleagues privately worry about Trump's “incompetence” and “ethics.”

Franken, whose profile is rising as a Trump antagonist and who has even gotten some 2020 buzz, was also asked about whether impeachment proceedings might be brought against Trump.

Franken's (apparently joking?) response:

“Let me remind you again that Republicans are in the majority. So I think it'll be — it's months and months away.”

(For the record, Article 2, Section 4 of the Constitution says: The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors. )

D.C. and Maryland plan to sue President Trump for violating a little-known constitutional provision called "the Emoluments Clause." (Jenny Starrs/The Washington Post)