Facebook CEO Mark Zuckerberg admitted on Wednesday that he was wrong to dismiss the idea that fake news shared on the giant social network affected last year’s presidential election.

Zuckerberg’s statement came in response to a tweeted attack from President Donald Trump hours earlier. Trump claimed that Facebook was “always anti-Trump” and accused it of colluding with news outlets that the president has deemed to be “fake news.”

“After the election, I made a comment that I thought the idea misinformation on Facebook changed the outcome of the election was a crazy idea,” Zuckerberg wrote on his Facebook page. “Calling that crazy was dismissive and I regret it. This is too important an issue to be dismissive.”

Shortly after the 2016 election, Zuckerberg had asserted at a tech conference that fake news made up “a very small amount of the content” on Facebook. He described as “a pretty crazy idea” the notion that fake news stories circulating on Facebook could have affected the election’s outcome.

Those remarks backfired on the tech billionaire this month after his company revealed that it was paid approximately $100,000 during the last election cycle to publish Kremlin-linked ads aimed at “amplifying divisive social and political messages across the ideological spectrum.”

Facebook was always anti-Trump.The Networks were always anti-Trump hence,Fake News, @nytimes(apologized) & @WaPo were anti-Trump. Collusion? — Donald J. Trump (@realDonaldTrump) September 27, 2017

..But the people were Pro-Trump! Virtually no President has accomplished what we have accomplished in the first 9 months-and economy roaring — Donald J. Trump (@realDonaldTrump) September 27, 2017

After Trump attempted to distance his electoral success from anything that happened on Facebook, Zuckerberg came out to defend his company’s “broader impact.” His post highlighted the role that Facebook played in getting more Americans involved in political discussions ahead of the election.

“More people had a voice in this election than ever before,” Zuckerberg wrote. “There were billions of interactions discussing the issues that may have never happened offline. Every topic was discussed, not just what the media covered.”

He noted that every presidential candidate had a Facebook page to speak directly to his or her base, adding that campaigns spent “hundreds of millions” to advertise on the site.

“That’s 1000x more than any problematic ads we’ve found,” he wrote.

Last week, Zuckerberg announced that Facebook would turn over copies of at least 3,000 ads ― however begrudgingly ― that were apparently linked to a Russian effort to influence the U.S. election.