A sequence of events that began with Russia annexing Ukraine picked up pace when Nancy Pelosi announced a formal inquiry

Nancy Pelosi, the House of Representatives speaker and the most powerful Democrat in Congress, announced an impeachment inquiry against Donald Trump on 24 September, setting off a fast-moving chain of events. Here are the key players, and here’s a timeline of the key moments in the scandal so far:

Refuse, block, stonewall – but Trump's strategy leaves little margin for error Read more

2014

Russia annexes Crimea, a peninsula in southern Ukraine. The military occupation, denounced by western powers, sparks the biggest east-west crisis since the cold war.

A popular uprising in Ukraine prompts the ouster of the Russian-backed president, Viktor Yanukovych.

Hunter Biden, son of Joe Biden (then vice-president of the US under Barack Obama, and instrumental in US-Ukraine policy) joins the board of the scandal-plagued Ukrainian energy company Burisma.

2016

Paul Manafort, chairman of the 2016 Trump presidential campaign, resigns less than four months before the US election, after Ukraine’s anti-corruption agency reveals he had been promised millions of dollars for undeclared consulting work for Kremlin-backed Yanukovych.

Manafort is later indicted for failing to register as a foreign agent and numerous financial offenses, and jailed. Trump has since pushed an unsubstantiated theory that the campaign of his 2016 political opponent, Hillary Clinton, played a role in the Ukraine-Manafort revelations.

2019

7 April Rudy Giuliani, Trump’s personal lawyer and former New York mayor, voices unsubstantiated allegations on Fox News that Joe Biden pressed for the dismissal of Viktor Shokin, a top Ukrainian prosecutor, in order to block a corruption investigation into Burisma. (The investigation into Burisma was dormant by the time the US, along with other western powers, called for Shokin to resign.)

22 April Volodymyr Zelenskiy, an actor and comedian with no political experience except for playing the president in a TV series, is elected Ukraine’s leader. Trump congratulates him in a phone call.

25 April Joe Biden announces his 2020 presidential campaign.

1 May The New York Times reports that Giuliani has been urging Ukraine to conduct a new investigation into the activities of Joe and Hunter Biden. “Giuliani called Mr Trump excitedly to brief him on his findings,” the paper says.

18 July Trump issues instructions to withhold $392m in military aid from Ukraine, citing concerns over whether the money needed to be spent, according to reports.

25 July Trump and Zelenskiy speak on the phone.

12 August A whistleblower complaint is filed.

13 September Adam Schiff, Democratic congressman and chairman of the House intelligence committee, issues a subpoena for the complaint after Joseph Maguire, the acting director of national intelligence, a Trump appointee, refuses to hand it over.

Days later, reports emerge that Trump asked Zelenskiy during the 25 July phone call to investigate Joe Biden and the candidate’s son, Hunter. Trump admits that he did, but denies wrongdoing. He denies that withholding aid had amounted to a quid pro quo. The aid funds were released on 11 September.

Trump, the whistleblower and the comic: key players in the Ukraine scandal Read more

19 September Giuliani is interviewed on CNN and in a heated exchange at first denies that he asked Ukraine to investigate Biden. About 30 seconds later, he reverses himself. “Of course I did,” he says.

24 September The House speaker, Nancy Pelosi, announces a formal impeachment inquiry into Trump’s actions.

25 September 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. “I don’t want to be involved in democratic elections of the USA,” Zelenskiy said. “Nobody pushed me.”

26 September The whistleblower complaint is released. It alleges the White House tried to cover up the Trump-Ukraine call.

27 September Kurt Volker, Trump’s former special envoy to Ukraine, resigns.

4 October The House congressional committees holding impeachment hearings release Whatsapp messages from US diplomats, handed over by Volker, which show a prestigious invitation for Zelenskiy to visit the White House was dependent on him stating publicly that Ukraine would investigate the Bidens and a supposed Ukrainian role in the 2016 US election, a theory advanced in far-right conspiracy circles.

6 October Lawyers for the first whistleblower say they are now representing a second.

8 October The state department prevents Gordon Sondland, US ambassador to the EU and a Trump donor, from testifying to a congressional impeachment hearing.

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.