Former General Michael Flynn offered his late-night resignation as it became clear Mr Trump would no longer tolerate the flurry of embarrassing revelations, including a claim that he was potentially vulnerable to Russian blackmail.
As Democrats demanded an inquiry into the links with Russia, of not just Mr Flynn but the entire Trump senior team, it became clear that Mr Flynn’s departure would not draw a line under the issue.
“The million dollar question is who knew what and when,” Professor Jeanne Zaino of Iona College, told The Independent. “Did the president know, and other than the president, who else knew, and sat on information for a month that the national security advisor was open to Russia?”
Mr Flynn, 58, had found himself at the centre of a gathering storm after it emerged he had spoken with a Russian diplomat about the issue of US sanctions before Mr Trump took office, and indicated the relationship between the two countries would improve under a new administration.
Sanctions had been imposed by Barack Obama in response to Russia’s alleged cyber-interference in the presidential election.
Mr Flynn had originally denied discussing sanctions, and senior officials including Mike Pence, had defended him. But when it emerged that US intelligence officials had been monitoring the call to the Russian Ambassador to Washington, Mr Flynn had to reverse course.
On Monday evening, the Washington Post reported that a month ago, the acting attorney general Sally Yates - an official whom Mr Trump subsequently fired - had informed the White House that she believed Mr Flynn had misled senior administration officials about the nature of his communications with the Russian ambassador.
She warned that as a result of that, the national security advisor was potentially vulnerable to Russian blackmail. The paper said it was unclear what the White House legal counsel, Donald McGahn, did with the information Ms Yates passed on.
Democrats have seized on the developments and demanded to know not only precisely what Mr Flynn said to Russian Ambassador Sergey Kislyak, but also the extent of other links to Russia among senior administration officials.
Democratic Senator from Montana, Jon Tester, told CNN there was a need for an independent inquiry. “General Flynn may be the tip of the iceberg or he may not,” he said.
Congressman Adam Schiff, the senior Democrat on the House intelligence committee, said it was essential to discover that the president knew.
“There are tonnes of questions,” he said. “We need a thorough investigation.”
Many observers in Washington had suspected that Mr Flynn’s days in the job were numbered.
Mr Trump was asked about the controversy last Friday as he flew to Florida on Air Force One with Japanese premier Shinzo Abe. He claimed to have no idea what story journalists were even referring to.
“I don’t know about that, I haven’t seen it,” Mr Trump said. “What report is that? I haven’t seen that. I’ll look into that.”
On Monday evening, an hour after Ms Conway told reporters that Mr Flynn had the president's “full confidence”, the White House suggested the ground under the former general’s feet was not so solid.
The White House said Mr Trump was “evaluating the situation” involving Mr Flynn. The President’s spokesman, Sean Spicer, told reporters the president was speaking with Mr Pence and others about the matter, according to the Associated Press. At around 11pm, it was announced that Mr Flynn had resigned.
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