WASHINGTON — National security adviser Michael Flynn has resigned following reports he misled Vice President Mike Pence about contacts with a Russian diplomat, upending Donald Trump's White House team less than a month after the president's inauguration.

In a resignation letter, Flynn said he gave Pence and others "incomplete information" about his calls with Russia's ambassador to the U.S. The vice president, seemingly relying on information from Flynn, initially said the national security adviser had not discussed sanctions with the Russian envoy though Flynn later conceded the issue may have come up.

Such conversations would breach diplomatic protocol and possibly violate the Logan Act, a law aimed at keeping private citizens from conducting U.S. diplomacy. The Justice Department had warned the White House late last month that Flynn could be at risk for blackmail because of contradictions between his public depictions of the calls and what intelligence officials knew to be true based on routine recordings of communications with foreign officials who are in the U.S.

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Here's a timeline of the controversy, starting in late 2016.