White House National Security Advisor Michael Flynn abruptly resigned on Monday night, after reports suggested he lied to the Vice President and other top White House officials about his contacts with the Russian ambassador.

Flynn's status was considered perilous after it came out that he discussed sanctions on Russia with Ambassador Sergei Kislyak; this happened in the final weeks of the Obama administration in January, while Flynn was a private citizen.  It is against US law for private citizens to negotiate foreign policy with other governments.  In reporting his discussions, Flynn told VP Mike Pence that the sanctions didn't come up, misinformation that Pence repeated in national television appearances.  Pence now says he believes that Flynn lied to him.

After Trump was inaugurated weeks later, Obama administration lawyer Sally Yates stayed on for a few days as acting Attorney General.  In this capacity she was privy to the FBI's monitoring of Flynn's communications, which had led agents to believe that Flynn's behavior made him a potential blackmail target for Russian blackmail.  Yates delivered these concerns to the White House, but she was unceremoniously dumped after she directed Justice Department lawyers not to defend his bigoted executive order on immigration.

Flynn had all sorts of other problems, including a whack job of a son known for spreading bizarre, right-wing conspiracy theories.  He had already been forced out as director of the Defense Intelligence Agency (DIA) 2014 for his chaotic management style, abuse of underlings, and questionable relationship with facts. 

But Flynn then glommed on to Donald Trump, sharing a common view that Islamic Terrorism was a bigger threat than others in the intelligence community would acknowledge - a view that wrongly spilled over to Islam and Muslims in general.  The former spymaster quickly became one of Trump's most-loyal supporters.

In his resignation letter, which the White House emailed to reporters, Flynn said he had held numerous calls with foreign officials during the transition.  "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," he wrote.  "I have sincerely apologized to the President and the Vice President, and they have accepted my apology."