Pelosi launched inquiry on 24 September over allegations that Trump sought the help of a foreign country to harm a political rival * What is the House voting on and why is it important?Members of the media wait at the stairs for former US ambassador to Ukraine Marie Yovanovitch as she testifies in the impeachment inquiry into Donald Trump on Capitol Hill on 11 October. Photograph: Carlos Jasso/ReutersThe House speaker, Nancy Pelosi, announced an impeachment inquiry against Donald Trump on 24 September.Since then, House committees have been taking witness testimony about an alleged plot by Trump to use the power of his office to solicit interference from a foreign country, Ukraine, in the 2020 election.Democrats say that amounts to an abuse of power impeachable under the US constitution. Republicans have said Trump’s conduct was concerning but not impeachable.A vote to impeach Trump on the House floor, which would be held at the conclusion of televised hearings, could play out by the end of the year. If Trump is impeached, the Senate would hold a trial in which a two-thirds majority vote would be required to remove him from office.Here’s a timeline of key events so far: April and MayThrough his personal emissary, Rudy Giuliani, Trump applies pressure on Ukraine to announce investigations tied to Joe Biden and his son Hunter. The Ukrainian president-elect, Volodymyr Zelenskiy, meets with subordinates on 7 May to discuss how to stay out of it. 23 MayIn a White House meeting, Trump is unmoved by the enthusiasm of a delegation of officials freshly returned from Zelenskiy’s inauguration in Kiev. “He just kept saying: Talk to Rudy, talk to Rudy,” EU ambassador Gordon Sondland testified. “I don’t know what he meant. He kept repeating it, though, ‘They tried to take me down, they tried to take me down.’” 3 JulyLt Col Alexander Vindman, top adviser on Ukraine on the National Security Council, is made aware of the suspension of military aid for Ukraine. In testimony, Vindman said: “But by 3 July, that’s when I was concretely made aware of the fact that there was a hold placed by [Office of Management and Budget].” 10 JulyAt a dramatic White House meeting, Trump emissaries ask top Ukrainian officials to investigate Biden, shocking US national security officials. According to multiple accounts, after Sondland makes the Biden ask, then national security adviser John Bolton abruptly terminates the meeting, later calling it a “drug deal”. Mid-JulyThe Office of Management and Budget informs the Pentagon and state department that Trump has suspended $391m in military aid for Ukraine. According to testimony by senior diplomat in Ukraine Bill Taylor, “In a regular, NSC secure video conference call on 18 July, I heard a staff person from the Office of Management and Budget say that there was a hold on security assistance to Ukraine but could not say why.” 25 JulyTrump speaks on the phone with Zelenskiy, reminding him that “the United States has been very, very good to Ukraine” and then asking for a “favor”. Trump wants Ukraine to announce investigations designed to make Joe Biden look bad and to cast doubt on Russian tampering in the 2016 US election. Early August High-level Ukrainian officials are made aware of the suspension of US military aid meant to help in their fight against Russian forces, according to a New York Times report. 12 AugustA whistleblower complaint against Trump is secretly filed to the inspector general of the intelligence community. For six weeks, the Trump administration will block Congress from obtaining the complaint. 16 AugustA security council recommendation that aid for Ukraine be released is raised in a meeting with Trump, according to Vindman. But “the president didn’t act on the recommendation”. 27 AugustBolton visits Taylor in Kyiv. Taylor brings up his concerns about suspended military aid. Bolton is “very sympathetic”, Taylor later testifies, and tells him to send a cable directly to secretary of state Mike Pompeo raising his concerns. 1 September Bilateral meetings in Warsaw, Poland. In a “supplement” to his original testimony, Sondland says, “I now recall speaking individually with [Zelenskiy aide Andriy] Yermak, where I said that resumption of US aid would likely not occur until Ukraine provided the public anti-corruption statement that we had been discussing for many weeks.” 9 SeptemberTaylor texts Sondland: “As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign.” 11 SeptemberThe military aid is released. 24 SeptemberPelosi announces a formal impeachment inquiry, accusing Trump of “a betrayal of his oath of office, a betrayal of our national security and betrayal of the integrity of our elections”. 25 SeptemberThe White House releases a partial “transcript” of the 25 July call, hours before Trump’s first face-to-face meeting with Zelenskiy at the United Nations. It’s awkward. 26 SeptemberThe whistleblower complaint is released. Citing “more than half-a-dozen US officials”, it presents an accurate version of the Trump-Zelenskiy call and alleges that the White House tried to cover up the call. 4 OctoberKurt Volker, Trump’s former special envoy to Ukraine, testifies. Afterwards investigators release WhatsApp messages showing US diplomats pursuing a “deliverable” for Trump in Ukraine in the form of the Biden and 2016 election-tampering “investigations”. 8 OctoberThe White House releases a letter refusing to cooperate with the impeachment inquiry, and accusing Democrats of trying to reverse the result of the 2016 election. 14 October Fiona Hill, senior director for Europe and Russia in the National Security Council, testifies. She describes a shadow foreign policy in Ukraine run by Giuliani, describes the 10 July White House meeting, which she attended, and says Bolton told her to take her concerns to the top NSC lawyer. 17 OctoberSondland testifies. He says he took Trump at his word that there was no quid pro quo with Ukraine. He will later return to Capitol Hill to partially or fully reverse that testimony. 22 OctoberTaylor testifies. In a 15-page opening statement, he describes his concern to discover an “irregular, informal policy channel” by which the Trump administration was pursuing objectives in Ukraine “running contrary to the goals of longstanding US policy”. 29 October Vindman testifies. He describes his alarm at witnessing the White House subvert US foreign policy in favor of Trump’s domestic political agenda and says he took his concerns to the top NSC lawyer. 31 OctoberThe House votes on a resolution laying out a process to move impeachment from closed-door depositions to open hearings. Tim Morrison, senior director for Russian affairs at the National Security Council, testifies a day after announcing that he will resign his post in short order. 5 NovemberThe impeachment committees begin releasing testimony transcripts. The overlapping testimonies tell the same story, of demands by US officials of Ukraine steadily ratcheting up between May and September, from a demand to investigate corruption to a demand that “President Zelenskiy to go to a microphone and say ‘investigations’, ‘Biden’, and ‘Clinton’.” 13 NovemberPublic impeachment hearings are scheduled to begin with the testimony of ambassador Bill Taylor and deputy assistant secretary of state George P Kent. Ambassador Marie Yovanovitch is to follow on 15 November.