MSNBC's Lawrence O'Donnell retracted his explosive claim that Trump was indebted to Russian oligarchs - here's how the fiasco unfolded.

On Tuesday, MSNBC host Lawrence O'Donnell reported that "single source close to Deutsche Bank" said Trump's loans from the bank were cosigned by Russian oligarchs "close to Vladimir Putin."

"A source close to Deutsche Bank says Trump's tax returns show he pays very little income tax and, more importantly, that his loans have Russian co-signers," O'Donnell said in a tweet immediately before his broadcast.

"If true, that explains every kind word Trump has ever said about Russia and Putin," he added in the tweet.

MSNBC host Rachel Maddow appeared to be startled by O'Donnell's revelation.

"What," Maddow said during her program's handoff. "Really?"

The alleged ties to Russia is a sensitive topic for the Trump administration.

As the cloud of the former special counsel Robert Mueller's investigation loomed over Trump's presidency for nearly two years, his administration's policies towards Russia has been heavily scrutinized by Democrats in Congress and the public.

The president has been accused of neglecting his allies, including Ukraine, and cozying up with Russia, leading some lawmakers to call for an inquiry into his business ties with the country.

Congressional Democrats subpoenaed Deutsche Bank, Trump's longtime bank, as part of their investigation into his finances for potential conflicts of interests or financial wrongdoing.

Meanwhile, Republican lawmakers described the attempts as a partisan move and a means to "[weaponize] our nation's tax code by targeting political foes."

O'Donnell's media colleagues started asking questions about his scoop.

Although O'Donnell qualified his on-air claims by saying he did not know if they were true, it did little to abate the questions from his colleagues in the media.

"This is an explosive claim," BuzzFeed News bureau chief Jon Passantino tweeted. "Is NBC News backing up this reporting?"

"Hours after this report aired, MSNBC and NBC News still haven't published a written story on Lawrence's claim or posted video of this segment," Passantino added. "Seems a bit odd?"

NBC News later said it was not able to verify O'Donnell's reporting and that it did not see the bank records.

"So the natural question is: Why did it run on MSNBC prime time," CNN senior media reporter Oliver Darcy tweeted in response to NBC's findings.

Trump's team put NBC "on notice," sending a fiery letter to NBC executives.

One of Trump's attorneys wrote to the executives alleging its host had made "false and defamatory statements."

Attorney Charles Harder demanded NBC "immediately and prominently retract, correct and apologize for the aforementioned false and defamatory statements," within 24 hours.

Republican operatives and Trump's son Eric also weighed in.

"This was a reckless attempt to slander our family and smear a great company," Eric Trump, the president's son and Trump Organization executive, said on Twitter.

"Apologies are not enough when the true intent was solely to damage and cause harm," he added. "As a company, we will be taking legal action. This unethical behavior has to stop."

O'Donnell apologized: "I made an error."

The MSNBC host on Wednesday afternoon apologized for the reporting on the unverified claim.

"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," he said on Twitter. "I shouldn't have reported it and I was wrong to discuss it on the air."

In a brief statement on his Thursday evening show, O'Donnell announced MSNBC was retracting the story.

He took to the air on Wednesday and gave a formal apology:

"Last night on this show, I discussed information that wasn't ready for reporting. 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 simply 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 air. I was wrong to do so."

"This afternoon, attorneys for the president sent us a letter asserting the story is false. They also 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."

The incident bore some similarities to MSNBC's previous reporting on Trump's finances.

In 2017, MSNBC host Rachel Maddow teased that she had obtained Trump's tax returns and would be shining a light into his finances during her show. The documents were anonymously leaked to David Cay Johnston, an award-winning investigative journalist.

Trump is the first president to not release his tax returns since President Richard Nixon. The matter was of intense public interest amid news reports of previous business troubles and allegations of financial violations.

"BREAKING: We've got Trump tax returns," Maddow tweeted in March 2017, adding, "(Seriously)."

Maddow teased her scoop for most of her hour-long show, which included several commercial breaks before the supposed reveal.

Maddow eventually revealed a 1040 form of Trump's 2005 tax return, which included new information about his tax rate and income, but did not live up to the hype surrounding the incident.