After revelations that then acting Attorney General Sally Q. Yates warned the White House in late January that Michael Flynn had misrepresented the content of his calls with a Russian diplomat and could be vulnerable to blackmail, Flynn resigned as National Security Advisor.
Speculation had long swirled that Flynn discussed sanctions leveled against Russia by former President Barack Obama for its alleged interference in the U.S. presidential election, but Flynn denied wrongdoing and the White House stood behind the former three-star General, until the Washington Post, citing U.S. officials, revealed Yates was so concerned that Flynn might have been compromised she contacted the White House. Yates was fired by President Donald Trump shortly thereafter for not enforcing the president's controversial immigration ban.
When rumors first surfaced that Flynn had discussed the sanctions with Russian Ambassador Sergey Kislyak, Vice President Mike Pence said the National Security Advisor had assured him that the calls were innocuous, including well wishes for Christmas.
In his resignation letter, Flynn said he'd apologized to both the president and vice president and claimed to have "inadvertently briefed the Vice President-elect and others with incomplete information” about the calls.
Trump has named Lt. General Joseph Keith Kellogg as acting National Security Advisor.