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 US 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 expected to begin in mid-November, could play out by the end of the year. If Trump is impeached, the Senate would then hold a trial in which a two-thirds majority vote against Trump would be required to remove him from office.Here’s a timeline of key events so far:April and May Through his personal emissary, Rudy Giuliani, Donald 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.10 July At a dramatic White House meeting, Trump emissaries ask top Ukrainian officials to investigate Biden, shocking US national security officials. According to multiple accounts, after ambassador Gordon Sondland makes the Biden ask, the then national security adviser, John Bolton, abruptly terminates the meeting, later calling it a “drug deal”.Mid-July The Office of Management of the Budget informs the Pentagon and state department that Trump has suspended $391m in military aid for Ukraine.25 July Trump speaks on the phone with Zelenskiy Trump reminds Zelenskiy that “the United States has been very, very good to Ukraine” and then asks 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 them in their fight against Russian forces, according to a New York Times report.12 August A whistleblower complaint against Trump is secretly filed to the office of the inspector general of the intelligence community. For six weeks, the Trump administration will block Congress from obtaining the complaint.1 September Bilateral meetings in Warsaw, Poland. Sondland tells Zelenskiy assistant Andriy Yermak “that the security assistance money would not come until President Zelenskiy committed to pursue the Burisma investigation”, diplomat Bill Taylor testified. Burisma is a gas company that formerly employed Hunter Biden.9 September Taylor texts ambassador Gordon Sondland: “As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign.”11 September The military aid for Ukraine is released.24 September Pelosi 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 September The 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 September The 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 October Kurt 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 October The 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 (NSC), 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 October Gordon Sondland, the US ambassador to the European Union, testifies. He says that he took Trump at his word that there was no quid pro quo with Ukraine – but Sondland later returned to Capitol Hill to partially or fully reverse that testimony.22 October William “Bill” Taylor, a career ambassador who runs the US embassy in Kiev, testifies. In a 15-page opening statement, Taylor described 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 Army officer Alexander Vindman, the top Ukraine expert on the national security council (NSC), testifies. He describes his alarm at witnessing the White House subvert US foreign policy in favor of Trump’s domestic political agenda. Vindman took his concerns to the top NSC lawyer.31 October The House of Representatives votes on a resolution laying out a process to move impeachment from closed-door depositions to open hearings. Timothy Morrison, the senior director for Russian affairs at the National Security Council, testifies.