Michael flynn trumps security adviser resigns
You're referring to the controversy surrounding Michael Flynn, who served as the National Security Adviser (NSA) to President Donald Trump from January 20 to February 13, 2017.
Michael Flynn was a retired United States Army Lieutenant General who had previously served as the Director of the Defense Intelligence Agency (DIA) under President Barack Obama. Trump appointed Flynn as his NSA in December 2016, and he took office on January 20, 2017.
However, Flynn's tenure as NSA was short-lived. On January 24, 2017, it was reported that Flynn had spoken with the Russian Ambassador to the United States, Sergey Kislyak, on December 29, 2016, just days before Trump's inauguration. The conversation was about sanctions that the Obama administration had imposed on Russia in response to its interference in the 2016 presidential election.
The problem was that Flynn had denied having any conversations with Kislyak about sanctions, and the White House had initially denied that Flynn had discussed sanctions with the Russian ambassador. However, it was later revealed that Flynn had indeed discussed sanctions with Kislyak, and that he had also asked Kislyak to delay the release of a statement criticizing the sanctions.
On February 13, 2017, Flynn resigned as NSA, citing the "circumstances surrounding the information that has come to light regarding my phone conversations with the Russian ambassador and a TV commentator." The FBI had been investigating Flynn's conversations with Kislyak, and it was reported that Flynn had lied to Vice President Mike Pence and other administration officials about the nature of his conversations with the Russian ambassador.
Flynn's resignation was seen as a major blow to the Trump administration, and it sparked a wave of criticism and controversy. The FBI's investigation into Flynn's activities was later expanded to include allegations of money laundering and other financial crimes.
In December 2017, Flynn pleaded guilty to making false statements to the FBI about his conversations with Kislyak, and he agreed to cooperate with the special counsel's investigation into Russian interference in the 2016 election. Flynn's guilty plea was seen as a significant development in the investigation, and it marked the first time that a high-ranking Trump administration official had pleaded guilty to a crime related to the investigation.
In December 2018, Flynn was sentenced to 40 months in prison, with credit for the time he had already served. He was also ordered to pay a $100,000 fine and to cooperate with the special counsel's investigation.