Rep. Darrell Issa of California, the Republican congressman who chairs the committee conducting the hearing, tried to get Gruber to say his comments inadvertently revealed aspects of the law that the Obama administration preferred to go unsaid.
"Are you stupid?" Issa asked Gruber.
"I don' think so," Gruber said.
"Does MIT employ stupid people?" Issa continued.
Gruber said, "Not to my knowledge, no."
Issa then pressed home his point: "You did say that, in fact, if people knew the whole truth, they wouldn't have voted for it?"
"I made a critical mistake," Gruber said.
Gruber got some help from Democratic committee members, who talked about the millions of people who had obtained health insurance coverage due to Obamacare.
But the ranking Democrat on the committee, Rep. Elijah Cummings of Maryland, ripped Gruber for the "stupid, I mean absolutely stupid comments he made over the past few years."
"I'm extremely frustrated with Dr. Gruber's statements that were irresponsible, incredibly disrespectful and did not reflect reality, and were incredibly insulting," Cummings said.
He said Gruber's comments "gave Republicans a public relations gift in their relentless campaign to tear down the Affordable Care Act."