Here is a chronology of events in the Ukraine scandal, which has prompted the opening of an impeachment inquiry by the Democratic-led US House of Representatives into President Donald Trump

July 25

Mr. Trump holds a 30-minute telephone conversation with Ukraine’s new President Volodymyr Zelensky, a former professional comedian who was elected in May 2019. Earlier in July, Mr. Trump — without explanation — suspended hundreds of millions of dollars in military assistance to Ukraine, which had been approved by Congress. The aid is eventually released by the White House on September 11.

August 12

An anonymous whistleblower in the U.S. intelligence community files an internal complaint about the Trump-Zelensky call, describing it as a matter of “urgent concern”.

Also Read Whistleblower complaint | How the White House and Justice Department learned about the CIA officer

September 18

The Washington Post publishes a report about the whistleblower complaint, saying that it involves a “promise” made by Mr. Trump to a foreign leader.

September 19

Michael Atkinson, the Inspector-General of the Intelligence Community, testifies before the House Intelligence Committee about the whistleblower complaint, but declines to reveal its contents, saying that acting director of national intelligence Joseph Maguire has barred him from doing so.

Mr. Trump reacts for the first time, calling the Post story “fake news” and stating that when he speaks with foreign leaders, he is well aware that there are likely “many people” listening.

September 22

Mr. Trump confirms that he discussed Joe Biden, his potential Democratic rival in the 2020 presidential election, and Mr. Biden’s son, Hunter, in his call with Mr. Zelensky.

Mr. Hunter Biden served on the board of a Ukrainian gas company while his father was Vice-President, but has not been officially accused of any wrongdoing.

September 24

Amid a cascade of press reports that Mr. Trump pushed Mr. Zelensky to investigate the Bidens, Nancy Pelosi, Democratic Speaker of the House of Representatives, announces the opening of an impeachment inquiry of the President for abuse of power. “The president must be held accountable,” Ms. Pelosi says. “No one is above the law.”

Mr. Trump calls it “PRESIDENTIAL HARASSMENT.”

September 25

The White House releases a rough transcript of the Trump-Zelensky call. It confirms that the President repeatedly asked the Ukrainian leader to investigate the Bidens and to “look into” it with Rudy Giuliani, Mr. Trump’s personal lawyer, and with Attorney-General Bill Barr.

September 26

The House Intelligence Committee releases the whistleblower’s complaint, which accuses Mr. Trump of “using the power of his office to solicit interference from a foreign country in the 2020 US election”. It also accuses White House lawyers of seeking to “lock down” access to the call transcript because of its politically sensitive nature.

Ms. Pelosi and several 2020 Democratic presidential candidates accuse the White House of engaging in a “cover-up”.

September 27

House committees subpoena Secretary of State Mike Pompeo for Ukraine-related documents.

Kurt Volker, the U.S. special representative on Ukraine, resigns after Congress orders him to provide a deposition as part of the impeachment inquiry.

September 30

House Democratic leaders order Mr. Giuliani to turn over Ukraine-related documents by October 15.

October 1

Mr. Pompeo pushes back against the House subpoenas, accusing Democrats of trying to “bully” U.S. diplomats into testifying against the White House.

October 2

Mr. Trump steps up his personal attacks on Adam Schiff, the chairman of the House Intelligence Committee who is spearheading the impeachment probe, saying he should be arrested for “treason”.

October 3

Mr. Trump openly calls on China as well as Ukraine to investigate the Bidens and dismisses his Democratic opponents as “maniacs” pursuing “impeachment crap.”

Mr. Volker testifies behind closed doors on Capitol Hill.

Text messages between U.S. diplomats are released indicating the Trump administration tried to tie military aid to Ukraine to an investigation into the Bidens.

October 6

A second whistleblower, with first-hand knowledge of President Donald Trump’s dealings with Ukraine, has spoken with the intelligence community’s internal watchdog, the lawyer representing the official said on October 6.

October 7

Mr. Trump says that the impeachment inquiry against him is a scam and called for investigations against Democratic Congressional leader Adam Schiff, who is initiating the proceedings against him. | EU ambassador to be deposed as impeachment inquiry rolls on

October 11

Two foreign-born Florida businessmen who have helped Mr. Trump's personal lawyer Rudy Giuliani investigate political rival Joe Biden are arrested in a scheme to illegally funnel money to a pro-Trump election committee and other U.S. political candidates.

October 12

Former U.S. Ambassador to Ukraine Marie Yovanovitch has told House impeachment investigators that President Mr. Trump himself had pressured the State Department to oust her from her post and get her out of the country. | Insane impeachment witch hunt will fail: Trump

October 17

Acting White House Chief of Staff Mick Mulvaney admits that Mr. Trump had tied military aid for Ukraine to Kiev undertaking an investigation that would help Mr. Trump politically. Mr. Mulvaney’s stunning admission supports a key allegation in the House impeachment effort, that the President illicitly sought foreign political help as he seeks re-election next year.

October 22

Mr. Trump likens the impeachment investigation against him to a “lynching”, a racially charged word from the darkest days of America’s slavery legacy.

October 25

U.S. District Judge Beryl Howell orders the Justice Department to give the House secret grand jury testimony from special counsel Robert Mueller’s Russia investigation.

October 31

U.S. Congress formally opens a new, public phase of its corruption investigation into Mr. Trump as U.S. lawmakers voted for the first time to advance the impeachment process targeting the U.S. President.

November 2

Mr. Trump says that he would like Mr. Zelenskiy to visit the White House, and expected the Ukrainian leader to take him up on such an invitation.

November 3

The U.S. official whose whistleblower complaint led to the impeachment inquiry against Mr. Trump offers to communicate directly with Republicans on the intelligence committee leading the inquiry. The action is in response to Republican efforts, led by Mr. Trump, to unmask the whistleblower, a member of the U.S. intelligence community whose identity has not been released.

November 4

Witness transcripts in the impeachment probe are made public for the first time, with the former U.S. ambassador to Kiev telling investigators she felt threatened by the president in his call to Ukraine’s leader.

November 5

U.S. House of Representatives committees say they had asked Mr. Mulvaney, the acting White House Chief of Staff, to appear for a deposition on November 8, a request he intends to ignore.

November 6

U.S. Ambassador to the EU, Gordon Sondland, says he had told a Ukrainian official that military assistance to the country was tied to a commitment to open certain investigations at Mr. Trump’s behest, against his political rivals.

November 7

U.S. congressional committees meet for the first time with an adviser to Vice-President Mike Pence, but former national security adviser John Bolton fail to heed a request to appear.

November 9

There was no hinting around, it was a straight-out trade, two key White House officials tell impeachment investigators. If Ukraine’s new leader wanted an Oval Office welcome from Donald Trump — and he did — he would have to open a public probe into the President’s Democratic foe Joe Biden and his son. “There was no ambiguity,” said Lt. Col. Alexander Vindman, an Army officer assigned to the National Security Council, recounting an extraordinary day of meetings at the White House last summer.

November 13

Following witnesses’ closed-door testimony in October, the House Intelligence Committee begins public hearings. Testifying on live television, top envoy to Ukraine William Taylor states that he was told Mr. Trump cared more about the probe into the Bidens than he did about Ukraine.

November 15

Marie Yovanovitch, the former U.S. ambassador to Ukraine ousted by Mr. Trump earlier in the year, testifies under oath, stating that she felt intimidated as the President attacks her in real time via Twitter.

November 19

Lt. Col. Vindman, a respected member of the White House National Security Council, tells Congress Mr. Trump’s call with Mr. Zelensky was “inappropriate”, stating: “It is improper for the President of the United States to demand a foreign government investigate a US citizen and a political opponent.”

November 20

Gordon Sondland, the U.S. envoy to the European Union and a Trump ally, tells lawmakers he followed Trump’s orders in seeking a “quid pro quo” deal for Ukraine to probe Biden in exchange for a White House summit.

Mr. Sondland testified that far from being a rogue operation the attempt to pressure Mr. Zelensky to announce investigations was widely known by top officials, including Vice-President Mike Pence and Secretary of State Mike Pompeo.

“We followed the president's orders,” he said. He would not attest, however, to allegations that Mr. Trump froze $391 million in aid to add pressure on Ukraine although he came to presume that was the case.

November 21

President Donald Trump’s former Russia adviser Fiona Hill urges lawmakers in the House of Representatives impeachment inquiry not to promote “politically driven falsehoods” that cast doubt on Russia’s interference in the 2016 U.S. election.

Some Republican members of the committee have advanced a discredited theory, embraced by Mr. Trump and some of his allies in Congress and the conservative media, that Ukraine, not Russia, interfered in the last election.

“This is a fictional narrative that has been perpetrated and propagated by the Russian security services themselves,” says Ms. Hill, who until July served as the director for European and Russian affairs at the White House National Security Council.