Washington — For nearly three weeks, President Donald Trump knew his national security adviser, Michael Flynn, had lied to top administration officials, including the vice president, about conversations with the Russian ambassador to the United States, but he kept Flynn on as a pivotal member of his team.

During that time, Flynn briefed Trump on global issues, sat in on phone conversations Trump held with a variety of world leaders, helped craft foreign policy as a trio of allies — the prime ministers of Britain, Japan and Canada — visited Washington, and helped formulate the response on Saturday to a North Korea ballistic missile launch.

He was seated in the front row at a news conference Trump held with Canadian Prime Minister Justin Trudeau on Monday.

But between that news conference on Monday afternoon and 10 o’clock that night, Trump “lost trust” in Flynn over his lying about his contacts with Russian officials and what White House press secretary Sean Spicer called “a host of other issues” and demanded Flynn’s resignation.

On Tuesday, Spicer declined to say what those other issues might have been, and he did not explain why it took the president more than two weeks to determine that Flynn was no longer worthy of being trusted.

“I’m not going to get into the specifics of what the president’s thinking was, but I will just say … that it was an evolving and eroding process,” Spicer said. He did not mention that Trump’s decision to fire Flynn came less than two hours after The Washington Post published a story detailing that the Justice Department had warned the White House that Flynn had mischaracterized his conversations with the Russian ambassador, whose phones are routinely tapped.

The Justice Department warning said that contrary to Flynn’s account, the two men did discuss sanctions that former President Barack Obama had imposed on Russia on Dec. 29 to punish Russia for its alleged efforts to influence the outcome of November’s presidential election.

The FBI is investigating Flynn’s contacts with Russia and questioned him last month, according to news reports. Democrats in Congress, who called for a bipartisan investigation, quickly questioned why Trump delayed taking action.

“If anyone in the White House knew about Flynn’s vulnerability and chose not to act, they exercised inexcusably poor judgment that put the security of our country at enormous risk,” said Rep. Adam Smith, D-Wash., the top Democrat on the House Armed Services Committee.

Flynn defended himself in an interview with The Daily Caller. He insisted he broke no rules in his talks with the Russian ambassador, but was concerned about leaks of classified information.

“I haven’t been fighting back because I’m not that kind of guy,” the publication quoted Flynn as saying. “I’m behind the scenes. I’ve always been behind the scenes. But this is ridiculous. It’s so out of control. I’ve become an international celebrity for all the wrong reasons.”

Even Republicans acknowledged that more information was needed.

Senate Majority Leader Mitch McConnell, R-Ky., suggested the Senate Intelligence Committee, already examining Russian involvement in the November election, could take a look at the Flynn situation as well.

“They have the broad jurisdiction to do it and any questions as to why the president did what he did ought to be directed the White House,” he said.

Sen. Roy Blunt, R-Mo., a member of the Senate Select Committee on Intelligence, said “there are a number of unanswered questions that need to be answered.”

Trump has long been criticized for his admiring comments about Russian President Vladimir Putin and his ties to that country. The president has said he would consider lifting the sanctions imposed against Russia over its 2014 annexation of Crimea from Ukraine.

Earlier this month, the White House loosened financial sanctions against Russia’s powerful security agency that the Obama administration had imposed as punishment for Russia’s meddling in November’s presidential election and for the Crimea annexation.

On Tuesday, Spicer offered new information about what the White House knew and when in a raucous briefing for reporters in which nearly every question dealt with Flynn’s firing.

Spicer said that Flynn had faced tough questioning from White House officials about his conversation with Russian Ambassador Sergey Kislyak. After that, Spicer, on Jan. 13, and Vice President Mike Pence, on Jan. 15, told reporters that Flynn and the ambassador did not speak about sanctions. Spicer said that Flynn and Kislyak had exchanged text messages and phone calls on Dec. 25 and 28 in part to arrange a subsequent phone conversation between Trump and Putin.

“I talked to Gen. Flynn yesterday, and the conversations that took place at that time were not in any way related to the new U.S. sanctions against Russia or the expulsion of diplomats,” Pence said on Fox News.

The Justice Department notified the White House counsel’s office on Jan. 26 that Flynn had misled the vice president, Spicer said.

Spicer tried to blame the Justice Department for waiting until after Trump was president to warn him about the discrepancies between what the FBI had overheard and what Flynn had told Pence.

“I think the first question should be, where was the Department of Justice in this? They were aware of this,” he said.