By Eunice Esomonu, Tyler Machado, Kaitlyn Budion, Molly Callahan, and Gregory Grinnell

The third presidential impeachment trial in the history of the United States began in earnest on Tuesday, with the Senate considering two articles of impeachment against President Donald J. Trump. The House of Representatives voted toimpeach Trump, alleging that he misused the power of his office in his dealings with Ukraine’s leaders—events that began unfolding nearly six years ago. Here’s who’s involved, and how we got there.

February 2014: Ukrainian President Viktor Yanukovych loses power and flees to Russia as his government collapses. Soon after, Russia annexes Crimea from Ukraine. Later that year, former Vice President Joe Biden’s son Hunter Biden joins the board of Burisma Holdings Ltd. Petro Poroshenko is elected president of Ukraine, and in the following year, Viktor Shokin becomes Ukraine’s prosecutor general. At the time, George Kent, a U.S. deputy assistant secretary of state, raises concerns about Hunter Biden’s position but is told by a Biden staffer that the vice president does not have the “bandwidth” to deal with the matter.

Early 2016: Ukraine’s parliament votes to fire Shokin, following pressure from U.S. officials, including Vice President Biden, to remove him. Biden and other officials assert that Shokin is corrupt and isn’t investigating corrupt politicians, and the U.S.threatens to pull $1 billion in loan guarantees if he is not removed. Shokin is replaced by Yuri Lutsenko. At the same time, the owner of Burisma, Mykola Zlochevsky, falls under Ukraine’s corruption investigation. In November, 2016, Donald Trump wins the U.S. presidential election.

2017-19: Robert Mueller is appointed to investigate Russian interference in the 2016 U.S. presidential election, and indicts Paul Manafort, Trump’s former campaign chairman. In April 2018, Trump hires Rudolph Giuliani as his personal lawyer through the Russia investigation. In March 2019, the special counsel investigation ends and Mueller gives his final report to Attorney General William Barr. Barr releases a report that the investigation did not establish collusion between Russia and the Trump campaign.

April 2019: Volodymyr Zelensky is elected president of Ukraine. In May, U.S. ambassador to Ukraine Marie Yovanovitch is recalled following political attacks by right-wing Ukraine media. In May 2019, The New York Times reports that Giuliani is planning to travel to Ukraine to discuss the Biden probe and Mueller investigation, but the plan is met with backlash and the trip is canceled. On May 20, 2019 U.S. Energy Secretary Rick Perry, U.S. ambassador to the European Union Gordon Sondland, and former Special Envoy to Ukraine Kurt Volker attend Zelensky’s inauguration. In June 2019 ABC News reports that Trump says he would accept aid from foreign governments against his domestic political enemies.

August 2019: An anonymous whistleblower files a complaint to Michael Atkinson, the inspector general for the intelligence community, outlining quid pro quo of aid for investigation. The whistleblower details an “urgent concern” that Trump has been misusing the power of his office. According to the complaint, Giuliani spoke with Shokin in late 2018, and met with Lutsenko to ask about the Biden probe in early 2019. Trump tells Vice President Mike Pence not to attend Zelensky’s inauguration, according to the whistleblower.

July 2019: Ukraine officials meet with Perry, Volker, Sondland, and then-U.S. National Security Advisor John Bolton. Sondland attempts to request a specific investigation in exchange for a meeting between Trump and Zelensky, according to later testimony by Lt. Col. Alexander Vindman and Fiona Hill, who was a senior official in the U.S. National Security Council at the time

July 2019: Volker texts Andrey Yermak, an aide to Zelensky, to emphasize how important it is for Zelensky to announce he’ll launch investigations into the Bidens and a theory that Ukraine, not Russia, was the source of election interference. Volker implies that doing so could result in a potential White House meeting for Zelensky. Trump calls Zelensky, and appears to tie the
release of U.S. funding to the results of a Ukrainian investigation into the Bidens’ role in Burisma Holdings, according to transcripts released later. Trump also suggests that Barr would be working with Ukraine officials, and says that Yovanovitch was bad news.

August 2019: Politico reports for the first time that the Trump administration was withholding $250 million in military aid from Ukraine. In September, Sondland tells Yermak that military aid will not be released until Zelensky promises to pursue the Burisma investigation, as Taylor, Kent, and Sondland later confirm.

September 2019: The Trump administration releases nearly $400 million in aid to Ukraine that has previously been withheld. On Sept. 24, 2019, House Speaker Nancy Pelosi announces a formal impeachment inquiry of Trump. Two days later, the White House declassifies the anonymous whistleblower complaint, and House Intelligence Committee Chair Adam Schiff releases it to the public on Nov. 15; the White House releases an incomplete transcript of the call between Trump and Zelensky. On Oct. 10, Lev Parnas and Igor Fruman, associates of Giuliani, are indicted and arrested for charges of campaign finance violations related to the 2016 U.S. election. On Oct. 17, Mulvaney confirms a quid pro quo with Ukraine, but walks back the statement later in the day.

Oct. 31, 2019: The House votes 232-196 in favor of formalizing the impeachment inquiry and on Dec. 18, representatives pass two articles of impeachment: an abuse of power article that passes by a vote of 230-197-1, and an obstruction of Congress article that passes by a vote of 229-198-1. On Jan. 15, 2020 the House votes to send the articles of impeachment to the Senate. On Jan. 21 the third presidential impeachment trial in the history of the U.S. begins.