Lawrence O’Donnell fully retracted and issued a sober, on-air apology for making a blockbuster claim — based on one source who spoke only to him — that Russian oligarchs had co-signed Donald Trump’s massive loans from Deutsche Bank, which began in 1998 and lasted nearly two decades.

O’Donnell had made his potentially groundbreaking assertion at the start of his Tuesday night show and repeatedly added the caveat “if true” while discussing it. However, no one in the MSNBC or NBC news division had vetted or corroborated O’Donnell’s account prior to him airing it and, by Wednesday afternoon, the Last Word host acknowledged in a Twitter post that he had made an “error in judgment.”

He offered a more lengthy mea culpa to open his Wednesday night show.

“Last night on this show I discussed information that wasn’t ready for reporting,” O’Donnell said. “I repeated statements a single source told me about the president’s finances and loan documents with Deutsche Bank. Saying ‘if true’ as I discussed the information was not good enough. I did not go through the rigorous verification and standards process here at MSNBC before repeating what I heard from my source. Had it gone through that process I would not have been permitted to report it. I should not have said it on air or posted it on Twitter. I was wrong to do so. This afternoon, attorneys for the president sent us a letter asserting the story is false. They demanded a retraction. Tonight we are retracting the story. We don’t know whether the information is inaccurate. But the fact is, we do know it wasn’t ready for broadcast, and for that I apologize.”

Watch the video above, via MSNBC.