Eric Trump vowed that the Trump Organization will take legal action against MSNBC and Lawrence O'Donnell after the left-leaning host aired a singled-sourced, unverified report that President Trump had loans co-signed by Russian oligarchs.

"This was a reckless attempt to slander our family and smear a great company. Apologies are not enough when the true intent was solely to damage and cause harm. As a company, we will be taking legal action. This unethical behavior has to stop. @Lawrence @MSNBC," Eric Trump tweeted Wednesday night.

The threat of legal action came after the MSNBC host apologized earlier in the evening for what he called an “error in judgment” during his show on Tuesday night.

“Last night I made an error in judgment by reporting an item about the president’s finances that didn’t go through our rigorous verification and standards process. I shouldn’t have reported it and I was wrong to discuss it on the air. I will address the issue on my show tonight,” O’Donnell tweeted Wednesday afternoon.

MSNBC HOST LAWRENCE O'DONNELL ADMITS HE MADE 'ERROR IN JUDGMENT' IN AIRING CONTROVERSIAL TRUMP-RUSSIA REPORT

The liberal host’s mea culpa came just hours after the president’s legal team sent a harshly worded letter to NBC on Wednesday demanding an apology and retraction for what it called “false and defamatory, and extremely damaging” comments.

The letter, obtained by Fox News, was sent by Trump’s legal counsel to NBC Universal executives.

“We write concerning the false and defamatory statements published by Lawrence O’Donnell and NBC Universal,” the letter read.

“Demand is hereby made that Mr. O’Donnell and NBCU immediately and prominently retract, correct and apologize for the aforementioned false and defamatory statements.”

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The letter, written by Charles J. Harder, asked for NBC to confirm in 24 hours: “O’Donnell and NBCU will 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,” Harder added.

NBC News did not immediately respond to a request for comment.

The incident occurred on Tuesday night when O’Donnell and fellow far-left MSNBC host Rachel Maddow were discussing how Trump was “able to obtain loans when no one else would loan him any money” when he tossed out the unverified speculation.

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“I may have some information, in this next hour, which would add a great deal to their understanding of that, if true, and I’ll be discussing it here,” O’Donnell said. “I stress ‘if true,’ because this is a single source who has told me that Deutsche Bank obtained tax returns… this 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.”

A stunned Maddow leaned back in her chair and responded, “What? Really?”

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O’Donnell added, “that would explain every kind word Donald Trump has ever said about Russia and Vladimir Putin” if his information is accurate.

“These statements are false and defamatory, and extremely damaging. The only borrowers under these loans are Trump entities, and Mr. Trump is the only guarantor. Numerous documents for each of these loans are also recorded, publicly available and searchable online. Thus, actual malice can easily be proven based on your reckless disregard of the truth and unreasonable reliance on an alleged ‘source’ who you will not even identify in your story and likely is seeking to mislead you and the public for political reasons or other ulterior motives,” the letter read in response to O’Donnell’s report.

This is one of the reasons that a majority of Americans have lost trust in the media. — White House Press Secretary Stephanie Grisham

“You are officially on notice of this dispute and are required to undertake steps to affirmatively preserve, and not delete, any and all physical and electronic documents, materials, information, and data,” the letter said.

The letter concluded by stating that if NBC failed to retract the story and apologize, Trump would “pursue all available causes of action and seek all available damages and other legal remedies to the maximum extent permitted by law.”

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Earlier in the day, White House Press Secretary Stephanie Grisham blasted O’Donnell over the story.

“This is one of the reasons that a majority of Americans have lost trust in the media. Instead of applying ethics and standards to their reporting, journalists and left-wing outlets have weaponized the media, using it to attack and harass people with little to no regard for the truth,” Grisham told Fox News.

MSNBC’s primetime hosts have had a long history of running with unverified claims regarding Trump and Russia. “The Rachel Maddow Show” has plummeted to fifth overall among cable news programs after she dedicated substantial airtime since Trump’s victory over Hillary Clinton in 2016 to speculating about whether or not Trump colluded with Russia.

Viewers began turning away when Maddow’s collusion theory was discredited by former Special Counsel Robert Mueller's report and testimony. Ex-MSNBC host Krystal Ball even blasted her former colleague earlier this year for floating wild “Russian conspiracy theories” that blew up when Mueller didn’t substantiate them.

“Rachel Maddow, you’ve got some explaining to do,” Ball said on The Hill’s “Rising.”

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Ball noted that MSNBC and Maddow “built segment after segment, show after show, on building anticipation for a big reveal” that never arrived.

NBC News did not immediately respond when asked if O’Donnell’s report met its standards.

Fox News' Brian Flood contributed to this report.