Flynn's departure less than one month into the Trump administration marks an extraordinarily early shakeup in the president's senior team of advisers. Flynn was a loyal Trump supporter throughout the campaign, but his ties to Russia caused concern among other senior aides.
Flynn initially told Trump advisers that he did not discuss sanctions with the Russian envoy during the transition. Vice President Mike Pence, apparently relying on information from Flynn, publicly vouched for the national security adviser.
Flynn later told White House officials that he may have discussed sanctions with the ambassador.