NEW YORK --White House press secretary Sean Spicer said the president asked Michael Flynn to resign as national security adviser due to "eroding trust" after he misled the vice president over his calls with Russia's ambassador.
At a press conference Tuesday afternoon, Spicer said President Donald Trump needs to have complete trust in those in his administration. He said while there was no legal issue with Flynn's actions, there was the issue of trust.
"The level of trust between the President and Gen. Flynn had eroded to the point where he felt he had to make a change," Spicer said. "The president was very concerned that Gen. Flynn had misled the vice president and others."
Spicer said there had been "a series of other questionable instances" in Flynn's conduct that led to Trump losing confidence in him but he did not elaborate on what they were.
Trump must now fill the vital national security post after Flynn's resignation.
Flynn stepped down late Monday, ending days of speculation about his fate following reports that he had misled Vice President Mike Pence and other officials about his discussions with Russia prior to Trump's Jan. 20 inauguration.
Whoever emerges as Trump's choice will lead the National Security Council at a time when the young administration is grappling with a series of national security challenges, including North Korea's reported ballistic missile launch.
The White House is also dealing with fallout from the rocky rollout of one of Trump's executive orders on immigration, which has been blocked by the courts. The order was intended to suspend the nation's refugee program and bar citizens of seven Muslim-majority countries from entering the United States.
Trump named retired Lt. Gen. Keith Kellogg as the acting national security adviser, one of three candidates the president has under consideration:
RETIRED LT. GEN. KEITH KELLOGG
Kellogg had previously been appointed the National Security Council chief of staff and, along with Flynn, advised Trump on national security and foreign policy issues during the campaign. He had been considered for national security adviser before the post went to Flynn.
Kellogg was chief operating officer of the Coalition Provisional Authority in Iraq, the interim governing body following the fall of Saddam Hussein in 2003. He previously worked as executive vice president of research and technology for Virginia-based information technology firm CACI International, which works as a contractor for defense, intelligence and homeland security agencies.
The most audacious choice would likely be former CIA director David Petraeus. Petraeus, a retired four star general, was bounced from his position atop the intelligence agency in 2012 after he it was revealed that he passed on classified information to his biographer, who had also become his mistress.
But Trump during the campaign spoke sympathetically about Petraeus' plight despite his frequent criticisms of his Democratic opponent Hillary Clinton for mishandling classified materials. Petraeus was briefly under consideration to become secretary of State before Trump picked Exxon CEO Rex Tillerson.
RETIRED VICE ADMIRAL ROBERT HARWARD
Robert Harward, a Navy Seal, served as Deputy Commander of the United States Central Command when it was under the command of General James Mattis, who is now secretary of Defense. He served on the National Security Council for President George W. Bush and commissioned the National Counter Terrorism Center.
Upon retirement in 2013 after a nearly 40-year career in the Navy, Harward took a post as a chief executive officer for defense and aerospace giant Lockheed Martin in the United Arab Emirates. Trump has recently been in very public negotiations with Lockheed over the cost of its F-35 fighter jet program.
WLS-TV and the CNNW contributed to this report.