The impeachment inquiry into US president Donald Trump is based on a whistleblower’s report. It details Trump’s efforts to influence Ukrainian leader Volodymyr Zelensky to investigate Joe Biden, his potential political rival in the 2020 presidential election.

The whistleblower felt it was an “urgent concern,” arguing that in pressing a foreign power to interfere in a US election, the president was misusing his office for personal gain, and endangering national security.

To understand the case, let’s look back at key moments leading to the impeachment inquiry, and what’s happened since it was announced.

2014: The Bidens, Burisma, and the Revolution of Dignity

On April 21, then vice president Biden visited Ukraine to announce an aid package that was meant to loosen the former Soviet state’s reliance on Russian gas.

About a month later, Biden’s son, Hunter, joined the board of Ukrainian gas company, Burisma. It was adding influential American and European associates to its board to signal a Western bent after the “Revolution of Dignity” ousted pro-Russian president Viktor Yanukovych. Hunter told the New Yorker that his father only once discussed Burisma with him, saying, “I hope you know what you are doing.”

Burisma and its owner, Mykola Zlochevsky, were being investigated for corruption. Ukrainian and American officials say there’s been no wrongdoing by the Bidens, despite Trump’s claims that vice president Biden tried to quell the inquiry into Burisma.

2016: The rise of Trump and his Ukraine obsession

In 2016, Trump made Paul Manafort his presidential campaign chairman. But Ukrainian anti-corruption investigators reported that Manafort had quietly consulted with Yanukovych, the pro-Russian former president of Ukraine, before his overthrow. The Obama administration and the EU were opposed to Yanukovych. Manafort was replaced as campaign chair, and Trump won his bid for office.

Still, Trump never forgot that it was the Ukrainians who had provided the damaging information about his former campaign chairman’s links to Yanukovych. According to The New York Times, he became obsessed. The president reportedly “fretted and fulminated…angry over what he sees as Ukraine’s role in the origins of the investigations into Russian influence on his 2016 campaign.” He enlisted his personal attorney Rudy Giuliani to probe Ukrainian prosecutors for information, and press them to initiate politically beneficial inquiries.

2017-2018: Mueller and Manafort

In May 2017, special counsel Robert Mueller was appointed to investigate Russian interference in the 2016 US presidential election. Mueller also inquired into whether Trump thwarted his probe, and obstructed justice.

The investigation led to Manafort being charged with engaging in a conspiracy against the US, and acting as an unregistered agent of a foreign principal, among other crimes. He was accused of laundering millions of dollars, which were earned while working on behalf of Yanukovych. Manafort was convicted. He is serving two sentences in federal custody, and faces prosecution in New York state court for additional crimes.

2019: Damning reports

March.

On March 20, Ukrainian prosecutor general Yuriy Lutsenko told The Hill that when he met with US ambassador Marie Yovanovitch in 2017, she tried to influence his work. A month later, Lutsenko admitted this wasn’t true. But Yovanovitch was shortly thereafter recalled from her post, and Trump, in his July 25 phone call with Zelensky, insisted she was “bad news”.

On March 22, Mueller handed over his report to attorney general Bill Barr, who characterized it as clearing the president. Special counsel Mueller objected to this spin in a letter to Barr that became public in May, writing, “The summary letter the Department sent to Congress and released to the public…did not fully capture the context, nature, and substance of this Office’s work and conclusions.”

April.

Mueller’s redacted report was released widely on April 18. He concluded that the Russians interfered with the 2016 presidential election, and that some Trump campaign members met with Russian agents, but found no conspiracy. Mueller also reported on Trump’s possible obstruction of justice. He did not exonerate Trump. However, the special counsel didn’t charge him either. He claimed Justice Department guidance barred this, and left the matter to lawmakers. But there was insufficient political will to initiate an impeachment inquiry.

On April 21, five years to the day Joe Biden visited Ukraine, actor-turned-politician Zelensky was elected president. Trump called to congratulate him, and to press his own agenda, urging Zelensky to coordinate with Giuliani in his two pet investigations—the Bidens, and Ukraine’s role in getting Trump’s 2016 campaign chair into hot water. Zelensky referred to this call in his July 25 talk with Trump.

On Fox News on April 25, Trump said Barr would want to look into Ukraine’s involvement in the 2016 US presidential elections.

On April 29, the whistleblower learned that ambassador Yovanovitch had been recalled.

May.

On May 6, the State Department officially announced Yovanovitch’s assignment in Ukraine had ended “as planned.”

On May 10, Giuliani cancelled a previously publicized trip to Ukraine, saying Zelensky was surrounded by Trump’s enemies.

On May 14, Giuliani told a Ukrainian journalist that Yovanovitch was recalled because she opposed Trump, the whistleblower reported.

US officials attended Zelensky’s inauguration on May 20. Trump reportedly responded to positive accounts by saying Ukrainian politicians are “terrible people. They’re all corrupt and they tried to take me down.”

The whistleblower stated that in May and through July, “multiple US officials” expressed concern about Giuliani circumventing national security processes to directly meet with Ukrainian leaders. Meanwhile, others noted that the Ukrainians were given the impression Zelensky would have to “play ball” about the investigations when talking to Trump.

June.

Trump told ABC News that he’d likely take damaging information on a political rival from a foreign government rather than turning it over to the FBI without considering the contents. “I think you might want to listen, there isn’t anything wrong with listening. If somebody called from a country, Norway, [and said] ‘we have information on your opponent’—oh, I think I’d want to hear it.” He said that accepting such information would not amount to election interference. Observers said it was a sign that the special counsel’s investigation had no effect on Trump’s view of the propriety of taking foreign assistance for domestic political advantage.

July.

In mid-July, the whistleblower learned of a sudden change in US policy. Funding approved by legislators to support Ukraine in the face of Russian aggression had been halted. Members of the Ukrainian Caucus in Congress said the explanation they were given was “interagency delay.” Now it appears Trump delayed the aid to convince Zelensky to do his bidding, even personally ordering the funds withheld.

On July 24, Mueller testified in a series of hearings, which Trump would refer to in a phone call with Zelensky the next day. This took place right after Zelensky led his Servant of the People party (which is named after the TV sitcom that made him famous) to a massive victory in parliamentary elections.

Perhaps emboldened by the lack of clarity or purpose provided by the Mueller hearings to his political foes, Trump pressed Zelensky on the phone. The actual transcript of the July 25 call with the Ukrainian president was improperly stored on a special server for classified national security information, the whistleblower reported, just one sign that White House officials knew Trump’s exchange with Zelensky was problematic. The reconstructed record released on Sept. 24 shows that Trump urged Zelensky to inquire into the Bidens, the Ukrainian role in the 2016 US election, and also pressed him to talk to Giuliani and Barr.

August.

In early August Giuliani traveled to Madrid to meet with Zelensky adviser Andriy Yermak, according to the whistleblower.

On August 12, the whistleblower reported “an urgent concern” to the inspector general for national intelligence, Michael Atkinson.

Two weeks later, Atkinson deemed the report credible and passed it to the acting director of national intelligence Joseph Maguire, who had seven days to tell Congress about if if he agreed the information was urgent. But he did not.

September.

On Sept. 3, a Justice Department memo said the whistleblower complaint didn’t meet the statutory definition of “urgent concern.”

On Sept. 9, Atkinson reported to House intelligence committee chairman Adam Schiff, and disagreed with the Justice Department’s assessment. Schiff and intelligence committee colleagues announced an investigation into Trump’s Ukraine dealings.

On Sept. 11, the White House released $250 million to Ukraine, explaining the delay by saying the president was mulling how to use the funds to advance “American national security interests.”

On Sept. 17, Atkinson told the intelligence committee that Maguire and the Justice Department advised him against revealing the whistleblower report.

Two days later, Atkinson met with the committee without disclosing the complaint’s contents.

On Sept. 24, Nancy Pelosi announced a formal impeachment inquiry into Trump’s Ukraine dealings. The president contended it was an extension of the political “witch hunt” that led to Mueller’s investigation.

The next morning, the reconstructed record of the July exchange with Zelensky was released. Trump characterized it as a “very nice, no pressure, call.” He and Zelensky gave a joint press conference at the United Nations in New York, and Zelensky said “nobody pushed me,” to which Trump added, “There was no pressure.” But with the world watching and Trump beside him, the Ukrainian could hardly have said anything else.

On Sept. 26, Maguire testified about the whistleblower’s report, a version of which was released to the public. Maguire said he delayed turning it over due to executive privilege concerns but stood with the whistleblower, and for the report’s credibility.

Giuliani was subpoenaed (pdf) on Sept. 30. He must produce documents for the House intelligence committee by Oct. 15. In an accompanying letter (pdf) investigators explained their inquiry into “credible allegations” that Trump threatened national security by pressuring Ukraine to interfere with the 2020 elections and withholding funds, as well as Giuliani’s role in the president’s scheme to use his public office to “advance his personal political interests.”

What happens next?

There is much evidence to be collected before a vote on articles of impeachment can be taken in the House of Representatives if deemed appropriate. Should that happen, and if Trump were to be impeached, senators could opt not to convict.

What’s certain, however, is that in 2020, American voters will address the matter through the ballot box, finally revealing what they really think of the political intrigue.