Jonathan Gruber, professor at Massachusetts Institute of Technology (MIT), listens during a House Oversight Committee hearing in Washington, D.C., U.S., on Tuesday, Dec. 9, 2014. (Andrew Harrer/Bloomberg)

A gaffe, under the oft-cited Michael Kinsley rule, is when somebody in Washington accidentally speaks the truth. But what happens when frankness leads you to say something so monumentally stupid — the verbal equivalent of a pratfall, a face-plant into a mud pit — that “gaffe” doesn’t cover it?

In that case, you have Grubered yourself.

The originator of this maneuver, MIT professor Jonathan Gruber, came to Capitol Hill on Tuesday, summoned by House Republicans to explain his caught-on-tape remark that passage of Obamacare, on which he was a prominent consultant, relied on the “stupidity of the American voter.”

The denunciation of his remarks was brutal: “Glib, thoughtless . . . uninformed . . . mean and insulting . . . uncalled for in any contest . . . demeaning . . . inexcusable arrogance.”

And those were Gruber’s words. The lawmakers were less charitable.

The chairman of the House Oversight and Government Reform Committee, Darrell Issa (R-Calif.), likened the witness to “Forrest Gump, the ultimate in successful stupid men.”

“Are you stupid?” Issa asked the man behind the namecard reading, “Mr. Gruber, PhD”

“I don’t think so, no,” the bespectacled Gruber, slouched over the witness table, replied.

“Does MIT employ stupid people?”

“Not to my knowledge.”

“So you’re a smart man,” Issa continued, “who said . . . some really stupid things?”

Gruber accepted that characterization. A can of Coke Zero that he had placed on the floor next to his chair had fallen over.

Members of the House Committee on Oversight and Government Reform grilled Jonathan Gruber, an MIT economist and former adviser on the Affordable Care Act, for controversial comments he made about the law. (Julie Percha and Rebecca Schatz/The Washington Post)

Gruber wasn’t about to get a defense from Democrats. “Stupid — I mean absolutely stupid comments,” the panel’s top Democrat, Elijah Cummings (Md.) told the witness. “They were irresponsible, incredibly disrespectful and did not reflect reality.”

Nobody in the room seemed to question the stupidity of Gruber’s stupidity remark, or his claim that “this bill was written in a tortured way” to avoid it appearing to be a tax, or that “lack of transparency is a huge political advantage” because people didn’t know that “healthy people pay in and sick people get money.”

Instead, it became a game of Grubering. Republicans tried to Gruber Democrats by asserting that Gruber was a key architect of Obamacare and that his talk about passing the law deceptively was true. Democrats tried to Gruber the Republicans by tying the hapless professor to former Massachusetts Republican governor Mitt Romney, for whom Gruber also consulted. And Gruber continued to Gruber himself, refusing reasonable demands that he disclose all the government fees he had received. He conferred more than once with his lawyer and dodged questions by saying, “Take that up with my counsel” or “I don’t recall the total” — making it likely the committee will haul him back for another round of Grubering.

It was the last scheduled hearing under Issa’s chairmanship and an appropriately zany coda to a tumultuous tenure. Outside the Rayburn House Office Building, a tea party group was selling T-shirts with Gruber’s photo and the words “I’m with stupid.” When Cummings noted the new oil painting of Issa on the wall behind them and referred to the “hanging of your portrait,” Issa interrupted with an R-rated response: “Thank you for saying I was hung.”

This may explain why Issa, who hit his term limit as chairman of the high-profile panel, has been assigned to legislative Siberia: chairmanship of the Judiciary Committee’s intellectual property subcommittee.

For his final act, Issa did his best to Gruber Obama, calling Gruber a “critical player” in Obamacare. Over the administration’s objections, he seated him on a panel next to Marilyn Tavenner, the official overseeing Obamacare, and called them a “perfect pairing.” Other Republicans grilled Gruber on how many times he met with Obama (once) and went to the White House (no clue).

Democrats countered by trying to Gruber the Republicans. Rep. Gerald Connolly (Va.) quizzed Gruber on his visits to Romney offices (dozens) and meetings with Romney (also one). Cummings read aloud quotes from Romney praising Gruber.

But Democrats could not conceal the damage that Gruber had done to them and Obamacare. Cummings said it was a “public relations gift” to Republicans. “You wrapped it up with a bow.”

Gruber, in a geeky tenor, apologized, profusely and endlessly. No fewer than 14 times, he referred to his “inexcusable” remarks and insisted that he was “not the architect” of Obamacare and had no business offering political opinions.

Rep. Trey Gowdy (R-S.C.) asked Gruber to elaborate on his claim that legislation “passed because the American people are too stupid to understand the difference.”

Gruber groveled, saying he was “trying to make myself seem smart by insulting others.”

“So you’re a professor at MIT and you’re worried about not looking smart enough?”

“Yes.”

“Well,” said Gowdy, “you succeeded.”

Twitter: @Milbank

Read more from Dana Milbank’s archive, follow him on Twitter or subscribe to his updates on Facebook.