Congresswoman Maxine Waters is the first US politician to say on the record that the document, which alleges the Russian state has compromising sexual and financial information on the President, is genuine.
“We already know about the part about the coverage they have on him with sex actions is supposed to be true,” Ms Walters told US broadcaster, MSNBC. “They have said that’s absolutely true, some other things they kind of allude to.”
She did not provide evidence to back up her claim or reveal who had said it was "absolutely true".
Pressed for more information, she said: “You understand that I am saying the investigations must be done, the drilling down must be done. We must get to the facts of what it has been about.”
If the dossier was ever substantiated, she said that Mr Trump should then be impeached.
“I don’t think you can do the impeachment just because I think or others think," she said. "But I think if we do the investigations, that we will find the connections and I do think that impeachment will be necessary.”
Ms Waters' office later claimed she had not intended to suggest the dossier had been verified.
“She wasn’t talking about anything that’s not already in the public domain,” an aide said.
Ms Waters was referring to unsubstantiated allegations in the dossier compiled by a former British spy Christopher Steele.
It alleged that the Russian intelligence service, the FSB had videos and recordings of Mr Trump in a Moscow hotel with prostitutes – material that could be used to carry out blackmail.
Never intended for publication, it was compiled as oppositional research, first on behalf of Mr Trump's rivals for the Republican presidential candidacy and later for the Democrats.
But prior to President Trump being sworn in, the BuzzFeed decided to publish it in January, although it admitted it had not been able to verify its contents.
However, it claimed the existence of the dossier meant there was a clear public interest in publishing.
Mr Trump denounced it as “fake news” but the FBI had attempted to make a deal witht Mr Steele, a former MI6 agent, to obtain the contents of the memo.
The controversial orders Donald Trump has already issued
The controversial orders Donald Trump has already issued
1/9 Trump and the media
White House Press Secretary Sean Spicer takes questions during the daily press briefing
2/9 Trump and the Trans-Pacific Partnership
Union leaders applaud US President Donald Trump for signing an executive order withdrawing the US from the Trans-Pacific Partnership negotiations during a meeting in the Roosevelt Room of the White House in Washington DC. Mr Trump issued a presidential memorandum in January announcing that the US would withdraw from the trade deal
3/9 Trump and the Mexico wall
A US Border Patrol vehicle sits waiting for illegal immigrants at a fence opening near the US-Mexico border near McAllen, Texas. The number of incoming immigrants has surged ahead of the upcoming Presidential inauguration of Donald Trump, who has pledged to build a wall along the US-Mexico border. A signature campaign promise, Mr Trump outlined his intention to build a border wall on the US-Mexico border days after taking office
4/9 Trump and abortion
US President Donald Trump signs an executive order as Chief of Staff Reince Priebus looks on in the Oval Office of the White House. Mr Trump reinstated a ban on American financial aide being granted to non-governmental organizations that provide abortion counseling, provide abortion referrals, or advocate for abortion access outside of the United States
5/9 Trump and the Dakota Access pipeline
Opponents of the Keystone XL and Dakota Access pipelines hold a rally as they protest US President Donald Trump's executive orders advancing their construction, at Columbus Circle in New York. US President Donald Trump signed executive orders reviving the construction of two controversial oil pipelines, but said the projects would be subject to renegotiation
6/9 Trump and 'Obamacare'
Nancy Pelosi who is the minority leader of the House of Representatives speaks beside House Democrats at an event to protect the Affordable Care Act in Los Angeles, California. US President Donald Trump's effort to make good on his campaign promise to repeal and replace the healthcare law failed when Republicans failed to get enough votes. Mr Trump has promised to revisit the matter
7/9 Donald Trump and 'sanctuary cities'
US President Donald Trump signed an executive order in January threatening to pull funding for so-called "sanctuary cities" if they do not comply with federal immigration law
8/9 Trump and the travel ban
US President Donald Trump has attempted twice to restrict travel into the United States from several predominantly Muslim countries. The first attempt, in February, was met with swift opposition from protesters who flocked to airports around the country. That travel ban was later blocked by the Ninth Circuit Court of Appeals. The second ban was blocked by a federal judge a day before it was scheduled to be implemented in mid-March
SANDY HUFFAKER/AFP/Getty Images
9/9 Trump and climate change
US President Donald Trump sought to dismantle several of his predecessor's actions on climate change in March. His order instructed the Environmental Protection Agency to reevaluate the Clean Power Plan, which would cap power plant emissions
It has since been reported that US investigators have corroborated aspects of the dossier concerning conversations between foreign nationals.
Ms Waters is the most senior of the 12 black women in the US Congress which she was elected to in 1991. She has been a politician for more than 40 years.
A fierce critic of Mr Trump, she has previously called his friends and advisers who have ties to Russia or oil and gas interests “a bunch of scumbags”.
In February, she warned Mr Trump was “leading himself” to possible impeachment because of his alleged conflicts of interests and that he was creating “chaos and division”.
The Senate Intelligence Committee is considering requesting testimony from Mr Steels as it investigates whether Mr Trump’s associates worked with Russian hackers in attempts to influence the presidential election.Reuse content