WASHINGTON • The White House was warned in January that Mr Donald Trump's national security adviser Michael Flynn was vulnerable to Russian blackmail, a top former official told lawmakers as the issue of the US President's ties to Moscow returned to the spotlight.
Mr Trump hit back by dismissing suggestions that his team colluded with Russia as a "hoax", and calling the congressional investigations into Russia's interference in the United States election a taxpayer- funded "charade".
Former acting attorney-general Sally Yates, a Barack Obama appointee sacked by Mr Trump early in his presidency, took the stand alongside former director of national intelligence James Clapper during Monday's hotly anticipated three-hour hearing of the Senate Judiciary Committee.
Ms Yates confirmed reports that she had told the White House six days into Mr Trump's administration that Mr Flynn, a former military intelligence chief, had not been honest with Vice-President Mike Pence about his discussions with the Russian ambassador to Washington, leaving him vulnerable to leverage from Moscow.
It nevertheless took 18 days before Mr Trump, pressed by Mr Pence and others, dismissed the retired army lieutenant-general, who had advised him on security issues throughout the 2016 presidential campaign.
"We believed that General Flynn was compromised with respect to the Russians," Ms Yates told the hearing in her first public comments on the scandal which has dogged the opening months of Mr Trump's presidency.
"This was a problem because not only did we believe that the Russians knew this, but that they likely had proof of this information. And that created a compromise situation, a situation where the national security adviser essentially could be blackmailed by the Russians."
Ms Yates, who was fired on Jan 30 after defying Mr Trump over his contested travel ban, did not say what Mr Flynn discussed with Ambassador Sergey Kislyak in a number of phone calls last December, which were secretly monitored by US intelligence.
Mr Pence said in January that Mr Flynn denied those calls involved sanctions placed on Russia by the Obama administration in response to its election meddling.
Mr Trump has repeatedly branded the issue of Russian interference "fake news" despite the US intelligence community's conclusion that President Vladimir Putin himself was behind the meddling.
In tweets on Monday, Mr Trump doubled down on that stance. "The Russia-Trump collusion story is a total hoax, when will this taxpayer-funded charade end?" he fumed in one post, while in another, he targeted Ms Yates - claiming she had "said nothing but old news!" after earlier assailing her for allegedly leaking classified information.
Ms Yates' comments came after former Obama officials revealed that the outgoing president himself firmly warned Mr Trump against naming Mr Flynn as national security adviser, just two days after the Nov 8 election. Mr Obama had cautioned against Mr Flynn, whom he fired in 2014 as head of the Defence Intelligence Agency because of his poor record in administration and personnel management.
In separate testimony on Monday, Mr Clapper called Russia's interference in last year's election "a clarion call for vigilance and action against a threat to the very foundations of our democratic political system".
AGENCE FRANCE PRESSE