1:20 pm Update: The Last Word‘s Lawrence O’Donnell has tweeted that he made “an error in judgment” last night by mentioning that a lone source had told him that some of Donald Trump‘s Deutsche Bank loans had been co-signed by Russian oligarchs close to Putin.

Donald Trump‘s personal attorney Charles Harder has threatened NBCUniversal with a defamation suit over last night’s The Last Word with Lawrence O’Donnell report, during which O’Donnell stated that a “single source close to Deutsche Bank has told me that…Donald Trump’s loan documents there show that he has co-signers. That’s how he was able to obtain those loans. And that the co-signers are Russian oligarchs [close to Putin].”

“This would explain, it seems to me, every kind word Donald Trump has ever said about Russia and Vladimir Putin, if true, and I stress the ‘if true’ part of this.”

O’Donnell also tweeted this allegation.

Harder’s letter charges that O;Donnell and MSNBC had made “the false and defamatory statements that ‘Russian oligarchs’ co-signed loans provided to Mr. Trump by Deutsche Bank, and described these ‘co-signers’ as ‘Russian billionaires close to Vladimir Putin.’”

Harder is warning other journos not to repeat O’Donnell’s allegedly false statement.

MSNBC has so far declined comment; ditto Deutsche Bank.

Trump/Harder are demanding that O’Donnell and NBCU “immediately and prominently retract, correct and apologize for the aforementioned false and defamatory statements. Failure to do so will leave my clients with no alternative but to consider their legal options which could include immediate legal proceedings against Mr. O’Donnell and NBCU.

“Should that occur, my clients would pursue all available causes of action and seek all available damages and other legal remedies to the maximum extent permitted by law.”