Feb. 14 (UPI) -- President Donald Trump asked for the resignation of national security adviser Michael T. Flynn because he had lost trust in the retired three-star general, the White House said Tuesday.
During a news briefing, Trump spokesman Sean Spicer said the issue of trust was the only reason the president decided to move on from Flynn as his top White House adviser on national security.
Flynn, 58, had come under intense scrutiny Monday night for conversations he had with Russian ambassador Sergey I. Kislyak in December, during which he may have discussed potential economic sanctions against Moscow for the Kremlin's purported meddling in the American election.
Flynn had told Vice President Mike Pence that neither sanctions nor any other policy matters were discussed with Kislyak -- but later said he couldn't be sure those topics didn't come up.
Spicer said Tuesday that Flynn's remarks to Pence -- not the discussions with Kislyak -- were the reason Trump asked for his resignation.
"This was an act of trust -- whether or not he actually misled the vice president was the issue," the press secretary said, saying Trump's trust in Flynn had "eroded."
"That's it, pure and simple."
The press secretary's remarks represented a stark departure from an assertion Monday from Trump adviser Kellyanne Conway, who told MSNBC Flynn still had the president's "full confidence."
Spicer said that Flynn communicating with Kislyak, or any other foreign counterpart, even before he took office, is part of the national security adviser's job in preparing for the transition of power. Although Flynn has taken substantial criticism for potentially discussing sanctions, Spicer said White House counsel had investigated the matter and concluded there was nothing illegal about it.
"The first part of [the review] was clearly to understand the legal aspect of this. And that was simply concluded, there was no legal aspect," he said. "Then what happened is the president evaluated the trust aspect."
In response to Flynn's departure, Republican and Democratic lawmakers called for investigations into the circumstances surrounding the adviser's resignation.
Senate Majority Leader Mitch McConnell said the Senate Intelligence Committee will likely look into the matter.
"It's likely that General Flynn will be at some point asked to come and talk to the committee about both post-election activities and any other activities that he would be aware of," Sen. Roy Blunt, R-Mo., a member of the Intelligence Committee, said.
"Unfortunately, because of the fast pace of events, I inadvertently briefed the vice president-elect and others with incomplete information regarding my phone calls with the Russian ambassador," Flynn wrote in his resignation letter Monday night. "I have sincerely apologized to the president and the vice president, and they have accepted my apology."
In addition to his discussions with the Russian ambassador, Flynn was also scrutinized for a 2015 trip he took to Russia during which he attended a banquet and sat next to Russian President Vladimir Putin. U.S. officials have launched an investigation to see whether Flynn received any payment from the Russian government in exchange for the appearance -- a transaction that could have violated the Logan Act, which requires prior approval for such payments from Congress.
Flynn's abrupt resignation has strengthened Democrats' resolve to call for investigations into potential ties between Trump and Russia and the Kremlin's actions in the U.S. presidential election.
"The FBI must accelerate its investigation of the Russian connection with the Trump administration, and Congress must call for a bipartisan, independent, outside commission to fully investigate Russia's influence on the administration and the election," House Minority Leader Nancy Pelosi, D-Calif., said.
"It is clear that our task is more urgent than ever," Sen. Mark Warner, D-Va., vice chairman of the Senate Intelligence Committee, said in calling for a "thorough examination of contacts between Russia and individuals associated with political campaigns."
Republicans supported Flynn's resignation, but mostly stopped short of backing deeper inquiries into how far the Russian connections go.
"I'm not going to prejudge circumstances surrounding this. I think the administration will explain the circumstances that led to this," House Speaker Paul Ryan, R-Wis., said.
Sen. John McCain, though, broke ranks Tuesday and sided with Democrats on the issue.
"Gen. Flynn's resignation also raises further questions about the Trump administration's intentions toward Vladimir Putin's Russia, including statements by the president suggesting moral equivalence between the United States and Russia despite its invasion of Ukraine, annexation of Crimea, threats to our NATO allies and attempted interference in American elections," McCain, R-Ariz., said in a statement.
Spicer said Trump will evaluate potential successors to Flynn immediately. The post is being filled in the interim by Lt. Gen. Joseph Keith Kellogg, chief of staff for the National Security Council.