A timeline from Ukraine's 2014 revolution to President Donald Trump's push for a Ukrainian probe of former Vice President Joe Biden.
February 2014 Ukraine is thrust into violent revolution, with thousands of anti-government protesters marching on the capital, Kiev. As a result, the country's government is overthrown and its pro-Russian president, Viktor Yanukovych, is removed from office. He remains exiled in Moscow.
April 2014 Vice President Joe Biden leads a U.S. delegation to Kiev tasked with rooting out corruption and advocating for Ukraine to diminish its reliance on Russian oil. The Obama administration had pledged aid money to support a fledgling Ukrainian administration recovering from a revolution that ousted the country's previous leader.
"You have to fight the cancer of corruption that is endemic in your system right now," Biden told the Ukrainian parliament during the first of several post-revolution visits to the country. "And with the right investments and the right choices, Ukraine can reduce its energy dependence and increase its energy security."
(MORE: Biden sidesteps questions about his son's foreign business dealings but promises ethics pledge)May 2014 Within months of his dismissal from the Navy Reserves after testing positive for cocaine, the vice president's son, Hunter Biden, joins the board of Burisma, Ukraine's premier oil and gas company.
Hunter Biden and his associate at a business entity called Rosemont Seneca Partners -- where Hunter Biden was a managing partner -- both obtained board seats around the same time. According to banking records reviewed by ABC News, Seneca Partners began collecting $166,666 payments each month.
May 2014 The Obama White House deflects questions from ABC News Chief White House Correspondent Jonathan Karl about potential conflicts of interest in light of Hunter Biden's new role at Burisma and the vice president's diplomatic role with Kiev.
During a daily press briefing, press secretary Jay Carney said, "Hunter Biden and other members of the Biden family are obviously private citizens, and where they work does not reflect an endorsement by the administration or by the vice president or president."
(MORE: Inside President Donald Trump's push for Ukraine probe of Democratic rival)Feb. 2015 Ukrainian President Petro Poroshenko appoints Viktor Shokin, a former investigator in the prosecutor general’s office, as the country’s prosecutor general.
Sept. 2015 During a speech in Odessa, Ukraine, the then-U.S. ambassador to Ukraine, Geoffrey Pyatt, slammed the “failure of the institution of the Prosecutor General of Ukraine to successfully fight internal corruption.”
Dec. 2015 Vice President Biden threatens to withhold funding from Ukraine if Shokin is not fired.
During an appearance at the Council on Foreign Relations in 2019, the former vice president would later tout his record of fighting corruption by boasting about that threat to withhold a billion dollar U.S. loan guarantee to Kiev if Ukraine's President Petro Poroshenko failed to "take action against the state prosecutor" -- referring to Shokin.
"'I'm going to be leaving here in six hours,'" Biden would recall telling Poroshenko. "'If the prosecutor's not fired, you're not getting the money.' Well, son of a bitch, he got fired."
Feb. 2016 The IMF threatened to withhold aid to Kiev, citing “Ukraine’s slow progress in improving governance and fighting corruption,” according to Christine Lagard, the IMF’s managing director.
March 2016 Viktor Shokin is fired as prosecutor general, Ukraine's most senior law enforcement position.
The circumstances surrounding Shokin's 2016 dismissal have become central to the debate in 2019 over whether the vice president inappropriately called for Shokin to be fired.
In an interview with ABC News in April 2019, Shokin would later say he believed Biden pressured the government to fire him because he was leading an investigation into Burisma. But the assertion that Biden acted to help his son has been undercut by widespread criticism of Shokin from several high-profile international leaders, including members of the European Union and International Monetary Fund, who said Biden's recommendation was well justified. Once Shokin was removed, the European Union's envoy to Ukraine, Jan Tombinski, lauded the decision as "an opportunity to make a fresh start."
March 29, 2016 Once Shokin was removed, the European Union's envoy to Ukraine, Jan Tombinski, lauded the decision as "an opportunity to make a fresh start,” after Shokin’s alleged “lack of tangible results of investigations into serious cases.”
Dec. 1, 2017 In a press release, Burisma announces that all charges against the company and its president, Mykola Zlochevsky, were dropped by the Ukrainian prosecutor general's office.
Jan. and Feb. of 2019 According to the whistleblower complaint, which cites public reports, Giuliani “met on at least two occasions with Mr. [Yuriy] Lutsenko,” Shokin’s successor as Ukraine’s prosecutor general, “once in New York in late January and again in Warsaw in mid-February.”
(MORE: Biden decries reports about Trump, Ukraine's president)April 2019 Hunter Biden's directorship at Burisma expires and he decides not to renew his seat.
"In this political climate," he said in a statement to ABC News in June of 2019, "where my qualifications and work are being attacked by Rudy Giuliani and his minions for transparent political purposes, I have decided not to renew my directorship."
April 25, 2019 Joe Biden launches his 2020 presidential campaign.
Early May 2019 Rudy Giuliani, the president's personal attorney, announces plans to go and then abruptly cancels a visit to Ukraine to convince the Ukrainian government to reopen an investigation into Joe Biden's role in the dismissal of Shokin.
In a spate of television interviews on Fox News, Giuliani predicted that, "there's no way [Biden] gets from here to the election without this being investigated."
(MORE: WH considers releasing transcript of Trump call with Ukraine's president: Sources)May 16, 2019 Ukraine's then-prosecutor general, Yuriy Lutsenko, tells Bloomberg that he had found no evidence of wrongdoing by Joe Biden or his son, Hunter.
"I do not want Ukraine to again be the subject of U.S. presidential elections," Lutsenko said. "Hunter Biden did not violate any Ukrainian laws -- at least as of now, we do not see any wrongdoing. A company can pay however much it wants to its board."
June 13, 2019 President Trump tells ABC News' George Stephanopoulos that he would accept damaging information on his political rivals from a foreign government.
June 2019 Responding to questions about his son's foreign business dealings, Joe Biden's campaign for president tells ABC News exclusively that if Biden wins the White House he will issue an executive order on his first day in office to "address conflicts of interest of any kind."
June 2019 In a statement to ABC News in June, Hunter Biden said, "at no time have I discussed with my father the company's business, or my board service. Any suggestion to the contrary is just plain wrong."
July 2019 In an interview with The New Yorker, Hunter Biden said he only had one interaction with his father about joining Burisma: "Dad said, 'I hope you know what you are doing,' and I said, 'I do.'"
(MORE: 'Not at all' taking new impeachment talk seriously: Trump)Aug. 29, 2019 Ukrainian President Volodymyr Zelenskiy appoints Ruslan Riaboshapka as the country’s new prosecutor general.
Sept. 19, 2019 The Wall Street Journal reported that President Donald Trump pressured Ukrainian president Volodymyr Zelensky, "about eight times to work with Rudy Giuliani on a probe" into Joe Biden.
The July phone call with Zelensky is the subject of a whistleblower complaint filed with the Intelligence Community Inspector General in August, which eventually led Congressional Democrats to launch an impeachment inquiry.
Sept. 21 and 22, 2019 Joe Biden spends the weekend defending himself from Trump. In a statement, the Biden campaign called on the president to release the transcript from his July phone call with the Ukrainian president.
Biden also told reporters that he and his son never discussed Hunter Biden's business with Burisma, despite Hunter Biden's comments to The New Yorker in July that he and Joe Biden had discussed the matter once.
Sept. 23, 2019 During a visit to New York for the U.N. General Assembly, Trump doubles down on the Bidens' actions in Ukraine.
"The one who's got the problem is Biden. If you look at what Biden did, Biden did what they would like to have me do, except there's one problem, I didn't do it," Trump said. "What Biden did is a disgrace, what his son did is a disgrace."