The Post's Jose DelReal explains why Affordable Care Act architect Jonathan Gruber's year-old comments about the historic law have Republicans so angry. (Jose A. DelReal and Nicki DeMarco/The Washington Post)

Jonathan Gruber is probably having a hell of a day.

The MIT economics professor, best known until now for his key role advising the Obama administration on the Affordable Care Act, has come under attack after year-old video of a University of Pennsylvania panel surfaced that featured him referring to the "stupidity of the American voter" and a “lack of transparency” as crucial to the passage of the 2010 health reform law.

Those comments have struck a nerve on the right, with some of the law’s critics pointing to Gruber’s comments as evidence that the administration intentionally deceived the American public on the costs of the program.

It's a now-familiar position for Gruber, who has become a lightning rod for Obamacare-related controversy in recent months, thanks in large part to his central role designing the law and shepherding it through Congress.

The academic joined the Obama transition team in 2008, with the New York Times referring to him as "Mr. Mandate." Gruber was reportedly the central figure in convincing the president that a viable health care reform plan would have to include an individual mandate to buy insurance, eventually helping to shepherd the law from its theoretical early stages to its enactment.

Long before the Affordable Care Act took center stage, Gruber was already well known among health care experts. Several years before, in Massachusetts, he had worked with then-Gov. Mitt Romney on the state-level health care reform plan there. Gruber would subsequently compare the two plans in the national press during the 2012 presidential election between Obama and Romney, calling the individual mandate in Massachusetts similar to the national version required under the ACA.

Gruber apologized for his newly-resurfaced 2013 remarks Thursday, telling MSNBC's Ronan Farrow that they had been an “off-the-cuff” mistake, an attempt to lay out the way political calculations affected the law as it was being written.

“The comments in the video were made at an academic conference,” Gruber said. “I was speaking off the cuff and I basically spoke inappropriately and I regret having made those comments.”

This isn't Gruber's first controversy of the year. In July, another video of 2012 comments showed him saying that the federal government legally withholds funding from states that do not set up their own exchanges. The comments, which were made during a question-and-answer session two years ago, appeared to corroborate a claim by the law’s detractors that the federal government intentionally coerces the states into creating their own exchanges by withholding funding if states fail to do so.

“I think what’s important to remember politically about this is, if you’re a state and you don’t set up an exchange, that means your citizens don’t get their tax credits,” he is shown saying to a small audience. “But your citizens still pay the taxes that support this bill. So you’re essentially saying to your citizens, you’re going to pay all the taxes to help all the other states in the country.”

Critics of the law tore into Gruber at the time, while supporters distanced themselves from the comment. Gruber himself apologized for the comments, saying they were incorrect and, once again, "off-the-cuff."

“I honestly don’t remember why I said that,” Gruber told The New Republic in July. “I was speaking off-the-cuff. It was just a mistake. People make mistakes. Congress made a mistake drafting the law, and I made a mistake talking about it.”