Michael Flynn, President Donald Trump's national security adviser, resigned Monday night, becoming the first casualty of Trump's administration.
Flynn's resignation comes after scandal over a conversation Flynn had with the Russian ambassador to the United States about the sanctions former President Barack Obama imposed on the country over its role in hacks during the 2016 U.S. presidential election.
Flynn initially said he never discussed the sanctions with Russian Ambassador Sergey Kislyak. Vice President Mike Pence — who spoke to Flynn about the conversation — later vouched for Flynn in an interview with CBS.
In his letter of resignation, Flynn said he "inadvertently" briefed Pence with "incomplete information regarding my phone calls with the Russian ambassador." Flynn professed to have served "with the utmost of integrity and honesty."
"I am tendering my resignation, honored to have served our nation and the American people in such a distinguished way," Flynn wrote in his letter of resignation, which the White House released after 11 p.m. EST on Monday.
Flynn's resignation comes after a frenzied day at the White House over how to deal with the fallout over his conversation with Kislyak.
As of 4 p.m. EST, top Trump adviser Kellyanne Conway said Trump had "full confidence" in Flynn.
Not long after Conway's interview, White House press secretary Sean Spicer said Trump was "evaluating the situation."
Later Monday evening, the scandal continued to balloon, after news broke that former acting Attorney General Sally Yates had warned the Trump White House in late January that Flynn was not truthful about his communication with the Russian ambassador, adding that Flynn was vulnerable to being blackmailed by the Russians over that communication.
With Flynn's resignation, the White House announced that retired Lt. Gen. Joseph Keith Kellogg will serve as acting national security adviser.
Correction: Feb. 13, 2017
A previous version of this article misattributed a quote from Michael Flynn's letter of resignation.