But in a Senate hearing on Monday, the former acting attorney general produced just enough fresh intrigue to offer Democrats a new opening in the war of attrition they are waging against Donald Trump's presidency.
In her long-awaited first public accounting of her dealings with the Trump administration, Yates testified that she explicitly warned White House counsel Donald McGahn in January that former national security adviser Michael Flynn had been compromised and could be a target for Russian blackmail.
Her intervention provoked an awkward new question that the White House will now have to answer. Why did it then take 18 days for Flynn to be fired -- a step that only took place when The Washington Post reported he had lied to Vice President Mike Pence about his calls with Russia's envoy to Washington?
"The vice president was unknowingly making false statements to the public and ... we believed that General Flynn was compromised with respect to the Russians," Yates said. "We felt like the vice president and others were entitled to know that the information that they were conveying to the American people wasn't true."
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The revelations did not in themselves represent a development that could break open the mystery of Moscow's meddling with last year's election and increasingly vocal Democratic claims of collusion between
Russia and members of the President's inner circle.
But they did cast new doubt on Trump's judgment in choosing Flynn, a controversial Washington figure, for such a crucial job in the first place -- on a day when it emerged that outgoing President Barack Obama counseled him to pick another national security adviser.
And the Yates claims were also an apt metaphor for the long and corrosive drama over Russia. Like many other allegations, hers were enough to tarnish and raise suspicions about the administration's conduct, but were not sufficient to pitch it into an existential crisis.
It may also not be easy for the administration to discredit Yates. Her calm presentation and refusal to get riled by some Republican senators trying to knock her off her game made her come across as a credible witness.
The presence of her co-witness, Washington veteran and former Director of National Intelligence James Clapper, also had the effect of bolstering Yates' comments.
More substantively, her testimony to a judiciary subcommittee represented the latest incremental step yet toward a broader understanding of why so many links have surfaced between Trump world and Russia.
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Alone, her appearance didn't prove much. But collectively with the other multiple channels of investigation, it could add up to more. Still, Democrats must be frustrated that they still have not made serious claims about Russian collusion with the White House. And their repeated calls for a special counsel they have no power to task often serves to stress the futility of their minority status on Capitol Hill.
But if Trump's quick and dismissive reaction to her appearance is any guide, the Yates testimony put another dent in the administration's defenses.
"Sally Yates made the fake media extremely unhappy today -- she said nothing but old news!" Trump said in a volley of tweets, possibly designed as a head-fake away from the substance of the hearing.
He added: "The Russia-Trump collusion story is a total hoax, when will this taxpayer funded charade end?"
Investigation could run into next year
The answer to that question may not come for a long time yet -- not at least until the FBI probe into Russian interference in last year's election and possible links to the Trump campaign wraps up.
FBI Director James Comey has given no timeline for the investigation. And there are new signs that congressional investigations into the affair may linger deep into Trump's term.
CNN's Manu Raju reported Monday that a mountain of evidence and partisan disagreement mean it could be 2018 before the job is wrapped up. And even then, hopes are fading that there can be a bipartisan conclusion on the extent of Russian election meddling.
The White House downplayed the hearing by pointing out the lack of a smoking gun -- a reality that so far has been central to the administration's claims that the Russia story is an invention of Democrats smarting at losing the election.
"Remember, the bottom line with the Russia stuff is the question of collusion during the campaign," a White House official said.
"If there is any other observation to make beyond the fact that after roughly 11 months of inquiries, no evidence of collusion has been presented, it is that there are divisions among Democrats between those willing to admit there is nothing there and those who would rather score political points," the official said.
"President Obama's former Director of National Intelligence and his former acting CIA Director have both said they have seen no evidence of collusion. Clapper repeated his assertion today."
More questions for the White House
Still, in the short term, the testimony of Yates likely means another lost day ahead for the White House as it uses up time and political energy brushing off a new round of questions and allegations about ties to Russia.
No doubt White House spokesman Sean Spicer and Trump himself would much rather be talking about the House vote to repeal Obamacare last week or the President's debut foreign trip in a couple of weeks.
But instead, Spicer, and the President if he appears on camera Tuesday, will be pressed to answer a series of questions arising out of the Yates hearing. The most pressing one is why it took 18 days for Flynn to be let go, after the White House was told he was compromised.
During that time, Flynn was the most senior national security official in the West Wing, privy to every intelligence and foreign policy decision and secret, all the while, at risk of being blackmailed by Moscow, according to Yates.
Then there is the apparent contradiction between how Yates described her efforts to raise the alarm about Flynn and the White House's description of the encounters.
The former acting attorney general said that she walked McGahn through Flynn's conduct in two meetings, on January 26 and again on January 27.
She was understood to be referring to telephone calls between Flynn and Russian ambassador to Moscow Sergey Kislyak before Trump took office.
Strikingly, Yates warned that not only was Flynn not telling the truth about the calls, the Russians knew and could probably prove he was lying -- therefore opening him up to blackmail.
"The Russians can use compromising material in a variety of ways, sometimes overtly, sometimes subtly," said Yates.
'Lying to the FBI is a crime, correct?'
Monday's hearing was also a master class by Democrats in the use of innuendo and suspicion to maximize the political damage to the administration.
Yates for example testified that she had seen a readout of an interview Flynn gave to the FBI during January, before she headed to meet McGahn.
She would not comment on the substance of the interview but her comment allowed Democratic senators to lead her on a path that raised the unspoken possibility that Flynn had not only not told the truth to Pence, but to the bureau.
Flynn has requested immunity from congressional committees in order to testify about Russia issues, but has not so far been charged or accused of a crime.
But Sen. Richard Blumenthal of Connecticut deliberately raised the question of Flynn's possible guilt in an exchange with Yates.
"Lying to the FBI is a crime, correct?" Blumenthal asked.
"It is, yes," Yates replied.
"Violation of 18 United States Code 1001?" Blumenthal continued.
"That's right," Yates said.
"And it's punishable by five years in prison?" was the next leading question.
"Yes, it is."
Blumenthal again: "So, if Michael Flynn lied to the FBI, he had a ton of legal trouble facing him?
"He could face criminal prosecution if he lied to the FBI, yes."