WASHINGTON >> Former acting Attorney General Sally Yates told Congress today she bluntly warned the Trump White House in January that new National Security Adviser Michael Flynn “essentially could be blackmailed” by the Russians because he apparently had lied to his bosses about his contacts with Moscow’s ambassador in Washington.

The testimony from Yates, an Obama administration holdover fired soon after for other reasons, marked her first public comments about the concerns she raised and filled in basic details about the chain of events that led to Flynn’s ouster in February.

Her testimony, coupled with the revelation hours earlier that President Barack Obama himself had warned Donald Trump against hiring Flynn shortly after the November election, made clear that alarms about Flynn had reached the highest levels of the U.S. government months before. Flynn had been an adviser to Trump and an outspoken supporter of his presidential candidacy in the 2016 campaign.

Yates, appearing before a Senate panel investigating Russian interference in the election, described discussions with Don McGahn, the Trump White House counsel, in which she warned that Flynn apparently had misled the administration about his communications with Sergey Kislyak, the Russian ambassador.

White House officials, including Vice President Mike Pence, had insisted that Flynn had not discussed U.S.-imposed sanctions with Kislyak during the presidential transition period. But they asked Flynn to resign after news reports indicated he had lied about the nature of the calls.

“We felt like it was critical that we get this information to the White House, in part because the vice president was unknowingly making false statements to the public and because we believed that Gen. Flynn was compromised with respect to the Russians,” Yates said.

“To state the obvious,” she added later, “you don’t want your national security adviser compromised with the Russians.”

She said she was briefing the Trump White House so that they could take “the action that they deemed appropriate” and that she believed the Russians already had the same information.

Yates’ questioning by a Senate panel investigating Russian interference in the presidential election was just one portion of a politically charged day that began with combative tweets from Trump and continued with disclosures from Obama administration officials about a private Oval Office conversation between Obama and his successor.

Republican senators in the hearing repeatedly pressed Yates on an unrelated matter — her refusal to defend the Trump administration’s travel ban — and whether she was responsible for leaking classified information. She said she was not.

Trump shouldered into the conversation in the morning, tweeting that it was the Obama administration, not he, that had given Lt. Gen. Flynn “the highest security clearance” when he worked at the Pentagon. Trump made no mention of the fact that Flynn had been fired from his high position by the Obama administration in 2014.

Yates filled in new details of the events of Jan. 26, describing contacting McGahn in the morning and telling him she had something sensitive to discuss in person. Later that day, at the White House, she told him there was an alarming discrepancy between how Trump officials, including Pence, were characterizing Flynn’s contacts with Kislyak and what intelligence officials knew to be true based on recordings they’d reviewed.

The pair spoke several times over the next two days, with McGahn asking Yates how Flynn had fared during an interview with the FBI earlier that week — she did not answer — and why it was the concern of the Justice Department if White House officials had misled each other.

Flynn’s forced resignation followed media reports that he had discussed U.S.-imposed sanctions on Russia with Ambassador Kislyak, which was contrary to the public representations of the Trump White House.

Yates herself, a longtime federal prosecutor, was fired by Trump on Jan. 30 after refusing to defend his travel ban. James Clapper, director of national intelligence under Obama, also testified. He retired when Trump took office.

Separately today, former Obama officials said he had raised general concerns about Flynn with Trump and had told the incoming president there were better people for the national security post.

Trump’s press secretary Sean Spicer said in response that if Obama “was seriously concerned” about Flynn’s connections to Russia or other foreign countries, he should have withheld Flynn’s security clearance. Flynn served under Obama as defense intelligence chief before Obama dismissed him.

Trump repeatedly has said he has no ties to Russia and isn’t aware of any involvement by his aides in any Russian interference in the election. He’s dismissed FBI and congressional investigations into his campaign’s possible ties to the election meddling as a “hoax” driven by Democrats bitter over losing the White House.

After the hearing, Trump tweeted: “The Russia-Trump collusion story is a total hoax, when will this taxpayer funded charade end?”

The Associated Press reported last week that one sign taken as a warning by Obama officials about Flynn’s contacts with Kislyak was a request by a member of Trump’s own transition team made to national security officials in the Obama White House for the classified CIA profile of Kislyak.

The AP interviewed multiple former U.S. officials, most of whom spoke on the condition of anonymity in order to discuss sensitive national security information.

Yates’ warning about Flynn capped weeks of concern among top Obama officials, former officials told the AP. Obama himself told one of his closest advisers that the FBI, which by then had been investigating Trump associates’ possible ties to Russia for about six months, seemed particularly focused on Flynn.

Yates, a longtime federal prosecutor and Obama administration holdover, had been scheduled to appear weeks ago before the House intelligence committee, but that hearing was canceled.

The subcommittee meeting today is one of multiple congressional probes into the Russia interference, along with House and Senate intelligence panels. All the committees are led by Republicans.

White House Correspondent Julie Pace contributed to this report.