President Donald Trump faces a formal impeachment inquiry in the Democratic-controlled House after he asked the newly elected Ukrainian president to investigate one of his chief political rivals, former Vice President Joe Biden. Biden led the Obama administration's diplomacy in Ukraine while his son, Hunter, was on the board of directors of a gas company.
Trump says his own behavior was appropriate. His critics say he had withheld military aid to Ukraine while he pressured its president, Volodymyr Zelenskiy, on the Bidens. A whistleblower's complaint now before the Congress accuses Trump of "using the power of his office to solicit interference from a foreign country in the 2020 U.S. election." It further alleges that the White House engaged in a cover-up by hiding a transcript of the conversation on a computer server meant only for highly classified information.
Democrats have since raised questions about the roles of Secretary of State Mike Pompeo and U.S. diplomats, Vice President Mike Pence, Attorney General Bill Barr, Trump attorney Rudy Giuliani and others in the president's interactions with Ukraine.
Here are some of the affair's main characters as fast-moving developments unfold.
Click on each section to learn more.
Emilie Mutert contributed to this article.