WASHINGTON (Reuters) - U.S. diplomat Gordon Sondland told a Ukrainian official his country would likely not get nearly $400 million in security aid unless they pursued investigations demanded by President Donald Trump, revising earlier testimony to the Trump impeachment inquiry.

Sondland, the U.S. ambassador to the European Union, who initially testified in October to the Democratic-led congressional inquiry, offered new details to lawmakers on Monday after his memory was “refreshed.”

The details appeared to bolster the initial whistleblower complaint that led to the investigation by three U.S. House of Representatives committees. The testimony also corroborated other witnesses who said Trump sought to pressure the Ukrainians into conducting investigations that appeared to be aimed at helping his re-election campaign.

The impeachment inquiry is focused on a July 25 phone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to open an investigation into former U.S. Vice President Joe Biden and his son Hunter Biden.

Joe Biden is a leading contender for the Democratic nomination to run against Trump in the November 2020 election. Hunter Biden was on the board of Ukrainian energy company Burisma that had been investigated for corruption.

The White House said the Sondland transcript undermined the impeachment inquiry. White House spokeswoman Stephanie Grisham pointed to Sondland’s inability to say who ordered the aid to Ukraine be withheld and that he admitted he “presumed” there was a link between the demand for a statement from the Ukrainians and releasing the aid.

“No amount of salacious media-biased headlines, which are clearly designed to influence the narrative, change the fact that the president has done nothing wrong,” Grisham said in a statement.

Sondland sent a text message in September in which he said Trump insisted there was “no quid pro quos.”

In his new statement, Sondland said that by the beginning of September “in the absence of any credible explanation,” he concluded that the withheld aid was linked to Trump’s demand that Ukraine publicly acknowledge an investigation. Sondland has said he did not realize early on that the investigation was meant to target the Bidens.

“Resumption of U.S. aid would likely not occur until Ukraine provided the public anti-corruption statement that we had been discussing for many weeks,” Sondland said he told a Ukrainian presidential adviser.

Much of the early parts of the investigation by the committees, which include Democratic and Republican lawmakers, were conducted behind closed doors, but now the inquiry is moving into a public phase.

Sondland submitted the supplemental testimony on Monday after testimony by other officials, including Bill Taylor, the top U.S. diplomat at the embassy in Kiev.

‘THREE AMIGOS’

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Trump has denied wrongdoing and accused Democrats of unfairly targeting him in hope of reversing his surprise victory in the 2016 presidential election.

Democrats accuse Trump of misusing taxpayer dollars destined for a vulnerable U.S. ally for personal political gain. The security aid was approved by Congress to help Ukraine curb Russian-backed separatists in eastern Ukraine.

If the House votes to approve articles of impeachment - formal charges - the Republican-controlled Senate would then hold a trial on whether to remove the president from office.

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Senate Republicans have so far shown little appetite for removing the president.

“If it were today, I don’t think there’s any question it would not lead to a removal,” Republican Senate Majority Leader Mitch McConnell told reporters on Tuesday, adding that the duration of any trial would depend on how long senators want to take.

Congressional Democrats also released testimony from Kurt Volker, Trump’s former special representative for Ukraine negotiations. Volker detailed what he described as the role of Trump’s personal lawyer, Rudy Giuliani, as a conduit between Washington and Kiev.

Volker and Sondland, with Trump’s secretary of energy, Rick Perry, were known as the “three amigos,” responsible for Trump’s unofficial channel to Ukrainian government officials, witnesses testified.

Volker said his decision to resign on Sept. 27 was because of the impeachment inquiry.

“I didn’t think I would be able to go to Ukraine or meet with Russians and be able to carry out those duties in that way anymore,” he said. He also said he wanted to provide testimony “with as much candor and integrity as I possibly could.”

Separately on Tuesday, House investigators released text messages from Taylor in which he expressed concerns to Volker that he was “struggling” with a decision to take the top Ukraine job because he was worried whether anyone could “succeed with the Giuliani-Biden issue swirling for the next 18 months.”

In another message on Aug. 12, Taylor discussed a draft statement announcing that Ukraine was opening a “transparent and unbiased investigation of all available facts and episodes.”

The next day, Volker said that Ukraine should insert into the proposed statement that the planned investigation would include issues “involving Burisma and the 2016 elections” - a reference to a discredited theory that Ukraine, not Russia, was behind the interference in the 2016 U.S. election.