March 2014: Russia annexes Crimea, part of Ukraine.

April 2014: Hunter Biden, son of Joe Biden, joins board of Ukrainian natural gas company Burisma.

Aug. 21, 2018: Former Trump campaign manager Paul Manafort found guilty of fraud in taking out more than $20 million in loans after his work in Ukraine ended.

April 1, 2019: Ukraine Prosecutor General Yuriy Lutsenko alleges, without evidence, that Joe Biden sought to stop a criminal inquiry that involved his son.

June 12: Trump says he would want to hear if foreign governments offered him damaging data about 2020 opponents.

July 18: A top Pentagon official and U.S. diplomats hear that $400 million in military aid for Ukraine put on hold.

July 25: Trump and Ukraine President Volodymyr Zelensky speak by phone, with Trump asking him to “do us a favor” and investigate Trump’s opponents and the Biden family.

Aug. 12: A whistleblower filed a complaint with Inspector General Michael Atkinson about that call, alleging Trump had dangled a meeting with Zelensky in exchange for launching investigations into the Bidens.

Sept. 9: Atkinson informs the House and Senate Intelligence Committees about the complaint and that it was being blocked from being forwarded to Congress as required by law. Three House committees launch an investigation of efforts by Trump, Rudy Giuliani and others to pressure Ukraine to assist Trump’s re-election efforts. Bill Taylor, a top official in the U.S. Embassy in Ukraine, again expresses concern to envoy Kurt Volker and U.S. Ambassador to the E.U. Gordon Sondland that the administration is withholding financial support to Ukraine “for help with a political campaign.”

Sept. 22: Trump acknowledges that he discussed Joe Biden with the Ukrainian president during a July call.

Sept. 24: House Speaker Nancy Pelosi announces a formal impeachment inquiry into Trump.

Sept. 25: The whistleblower’s complaint is delivered to Capitol Hill. That same day, the White House releases a rough transcript of Trump’s July 25 call with Zelensky.

Sept. 26: The complaint is declassified and released to public.

Oct. 2: Secretary of State Mike Pompeo says he was on the July 25 call and defends it.

Oct. 8: The White House tells House Democrats that it will not cooperate with the impeachment inquiry.

Oct. 22: Taylor testifies that Sondland told him U.S. aid was contingent on Ukraine’s promise to investigate.

Nov. 20: Sondland testifies there was a quid pro quo involving Ukraine.

Dec. 5: Pelosi says House committees will draft articles of impeachment.

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