Michael Flynn timeline: How and why did Trump's key adviser resign?
Donald Trump's national security adviser, Michael Flynn, has resigned over his contacts with Russia, after just three weeks and three days in the job.
It is alleged that he discussed diplomatic issues with the Russian ambassador to the US before assuming his role at the White House.
It is illegal for private citizens to conduct US diplomacy.
The issue has been a communications nightmare for Mr Trump's top team.
Here is a round-up of how events have escalated.
18 November 2016: Michael Flynn is announced as the next US national security adviser, despite major questions over his links to Russia. His role, as part of the president's executive office, does not require approval from the Senate
28 December: Mr Flynn and the Russian ambassador to the US, Sergey Kislyak, exchange Christmas text messages
29 December: US President Barack Obama announces sanctions expelling 35 Russian diplomats for the country's alleged interference in the US presidential elections
29 December: Mr Flynn holds a phone call with the Russian ambassador
15 January 2017: Vice-President Mike Pence says, on US television network CBS, that he had spoken to Mr Flynn about the phone call and can confirm that it had "nothing whatsoever to do with those sanctions"
20 January 2017: President Trump and his executive team, including Mr Flynn, take office
22 January: The Wall Street Journal reports Mr Flynn is under investigation by US counterintelligence
26 January: The Justice Department contacts the top lawyer in the White House, Donald McGahn, about Mr Flynn's communications with Mr Kislyak, warning that Mr Flynn may be vulnerable to Russian blackmail. Mr McGahn informs Mr Trump. At the president's request, White House lawyers conduct a review. After questioning Mr Flynn on "several occasions", they conclude there were no legal issues with the call
8 February: Mr Flynn, in an interview with the Washington Post, denies discussing sanctions with the Russian ambassador
9 February: Mr Flynn's spokesman backs away from the denial, saying Mr Flynn "indicated that while he had no recollection of discussing sanctions, he couldn't be certain that the topic never came up"
10 February: President Trump tells reporters aboard Air Force One he has not seen the reports about Mr Flynn. "I don't know about that. I haven't seen it," he says
11/12 February: Mr Flynn spends the weekend at Mar-a-Lago, Mr Trump's Florida estate, alongside the president and Japanese Prime Minister Shinzo Abe. The Trump administration faces its first international crisis: a North Korean missile launch
12/13 February 2017: Stephen Miller, President Trump's top policy adviser, declines to say when asked in a number of interviews whether Mr Trump backed Mr Flynn
13 February 2017:
- Kremlin spokesman Dmitry Peskov says Mr Flynn and Mr Kislyak did not discuss lifting sanctions
- When asked about if Mr Flynn discussed sanctions with the ambassador, President Trump's spokesman, Sean Spicer, says: "No, absolutely not. No way"
- Mr Trump's senior aide Kellyanne Conway says Mr Flynn has the president's "full confidence"
- Shortly after Ms Conway's television interview, Mr Spicer announces that Mr Trump is "evaluating" Mr Flynn
- Mr Flynn resigns. In his resignation letter, he writes: "I inadvertently briefed the vice-president elect and others with incomplete information regarding my phone calls with the Russian ambassador"