Donald Trump was doing well at the GOP Debate on Wednesday evening until a blunder in which he claimed not to have called Marco Rubio “Mark Zuckerberg’s personal senator.”

Moderator Becky Quick–who had been aggressive with all of the candidates–asked Trump about the quote in the context of his policy on H1-B visas for skilled immigrants.

Trump denied having said the line: “”I never said that.” He then suggested that Jeb Bush may have been to blame for the quote, and accused the moderators of “really doing some bad fact-checking.”

Quick apologized, though it was not clear she was convinced.

In fact, Trump used the line in his immigration policy, in which he called for H1-B visa recipients to be paid the prevailing wage, so that they did not undercut American workers: “Mark Zuckerberg’s personal Senator, Marco Rubio, has a bill to triple H-1Bs that would decimate women and minorities.”

Breitbart News highlighted the remark at the time.

Trump went on to tell Quick that he was in favor of visas that would allow the U.S. to retain skilled science and technology graduates from abroad, alongside his policy against illegal immigration.

Update: Quick came back from a commercial break to point out that Trump’s quote was on his own website. She gave him an opportunity to explain himself. He expanded on his immigration policy, saying he was in favor of legal immigration.

It is not clear how much damage Trump suffered from the error, as the moderators had already discredited themselves in the eyes of many of those watching with a series of harsh questions based on opposition research.