What did the president know, and when did he know it? 

Source: https://www.washingtonpost.com/news/the-fix/wp/2017/02/14/the-timeline-of-michael-flynns-resignation-is-troubling-for-the-trump-white-house/?utm_term=.219ea3914da6

• Dec. 29: Flynn, a former lieutenant general who had been selected as Trump's national security adviser, speaks to Russia's ambassador to the United States, Sergey Kislyak. Despite Flynn's later denial and the White House's later comments, he and Kislyak discuss sanctions and the possibility of relieving them once Trump is president — even as the Obama administration was announcing new sanctions for Russia's alleged meddling in the 2016 election.
• Jan. 12: For the first time, Flynn's talks with the Russian ambassador are reported by Post columnist David Ignatius. Few details are known, but Ignatius notes that if the two discussed the sanctions, this could violate an obscure law known as the Logan Act, which prohibits unauthorized citizens from dealing in disputes with foreign governments.
• Jan. 13: In his first comments on the matter, Spicer says Flynn told him that he had exchanged text messages with Kislyak before they spoke on Dec. 28. (The date was later corrected to Dec. 29.) But Spicer said it was only to discuss logistics for a call between Russian President Vladimir Putin and Trump after Trump was sworn in as president. “That was it, plain and simple,” Spicer said.
• Jan. 14: Flynn assures Pence, who was then the vice president-elect, that the two of them didn't discuss sanctions, according to Pence.
• Jan. 15: Pence says on the Sunday shows that Flynn and Kislyak didn't discuss sanctions. “I talked to General Flynn yesterday, and the conversations that took place at that time were not in any way related to the new U.S. sanctions against Russia or the expulsion of diplomats,” Pence says on “Fox News Sunday.”
• Jan. 26: The Justice Department, then headed by acting attorney general Sally Yates (whom Trump would later dismiss for not defending his travel ban), informs White House counsel Don McGahn of Flynn's misleading statements. It also warns that they were so egregious that he could open himself up to Russian blackmail, given Russia knew he had mischaracterized the call to his superiors, according to Washington Post reporting. Spicer confirmed the specific date on Tuesday. “The first day that the Department of Justice … sought to notify White House counsel was January 26,” Spicer said. “The president was immediately informed of the situation.” Spicer said the White House didn't believe Flynn had violated the law. None of this was disclosed publicly at the time.
• Feb. 8: In an interview with The Post that would be published the following day, Flynn categorically denies having discussed sanctions with the Russian ambassador.
• Feb. 9: The Post reports that Flynn did, in fact, discuss sanctions with the Russian ambassador. In response, a spokesperson amends Flynn's denial, saying that he “indicated that while he had no recollection of discussing sanctions, he couldn’t be certain that the topic never came up.”
• Feb. 10: Trump says in brief comments aboard Air Force One that he is unaware of The Post's report but that he will “look into” it.
• Around 5 p.m. Monday: Conway says the White House has “full confidence” in Flynn and seems to excuse him for having forgotten that he discussed sanctions with the Russian ambassador.
• Also around 5 p.m. Monday: Spicer issues a contradictory statement. “The president is evaluating the situation,” he said. “He's speaking to the vice president relative to the conversation the vice president had with Gen. Flynn, and also speaking to various other people about what he considers the single most important subject there is: our national security.”
• 8 p.m. Monday: The Post reports that the Justice Department had told the White House last month “that Flynn had so mischaracterized his communications with the Russian diplomat that he might be vulnerable to blackmail by Moscow.”
• Shortly before 11 p.m. Monday: Flynn resigns.
• Tuesday morning: Conway says Flynn resigned voluntarily.
• Tuesday afternoon: Spicer, again contradicting Conway, says Trump requested the resignation: “Whether or not he actually misled the vice president was the issue, and that was ultimately what led to the president asking for and accepting the resignation of General Flynn. That's it. Pure and simple, it was a matter of trust.”