A key witness in President Donald Trump's impeachment investigation has dramatically revised his sworn testimony, acknowledging that he told a senior Ukrainian official that nearly $400 million in American military assistance would likely remain frozen until Ukraine publicly committed to investigations sought by Trump.

Gordon Sondland, the U.S. ambassador to the European Union and a major Trump campaign donor, submitted the revised account after testimony from other witnesses contradicted his earlier statements.

The reversal, revealed Tuesday when House investigators released Sondland's deposition transcript, provides significant new evidence supporting allegations that the Trump administration used American foreign assistance to pressure Ukraine into investigations that could benefit the president politically.

Ambassador Changes His Story

Sondland originally testified on October 17 that he could not recall knowing military assistance was conditioned on Ukrainian investigations.

But in a supplemental declaration submitted Monday, Sondland acknowledged that other witnesses had refreshed his memory.

He now recalls a September 1 conversation in Warsaw with Andriy Yermak, a senior adviser to Ukrainian President Volodymyr Zelensky.

During that conversation, Sondland said he warned Yermak that American military assistance would likely remain suspended until Ukraine issued a public anti-corruption statement.

The proposed announcement involved investigations into Burisma, a Ukrainian energy company that employed Hunter Biden, the son of former Vice President Joe Biden, and allegations concerning interference in the 2016 American election.

Joe Biden is a potential Democratic challenger to Trump in the 2020 presidential election.

New Questions About Trump's Denials

Trump has repeatedly insisted there was no improper exchange involving military assistance and investigations.

Sondland's revised testimony complicates that defense by establishing that a senior American diplomat communicated such a connection directly to a Ukrainian official.

However, Sondland acknowledged that he did not know precisely why the assistance had been suspended. He said he presumed the delay was connected to the requested public announcement.

The White House seized on that distinction Tuesday.

Press Secretary Stephanie Grisham argued that Sondland's revised account did not establish that Trump personally ordered the assistance withheld in exchange for investigations.

Nevertheless, the ambassador's admission closely resembles accounts provided by other diplomatic officials who have described growing pressure on Ukraine.

Giuliani's Role Under Scrutiny

The testimony also raises additional questions about Rudy Giuliani, Trump's personal attorney, who has been deeply involved in efforts to persuade Ukrainian officials to announce investigations.

Sondland previously testified that Giuliani's demands became increasingly troubling as diplomatic discussions progressed.

Investigators are examining whether official American foreign policy was being used to advance the president's personal political interests.

The White House meeting sought by Zelensky was also reportedly conditioned on Ukraine publicly committing to the investigations.

Impeachment Investigation Intensifies

House Democrats released Sondland's testimony alongside that of former special envoy Kurt Volker as the impeachment investigation moves toward public hearings.

The central question remains whether Trump improperly used the powers of the presidency to pressure a foreign government into investigating a domestic political rival.

Sondland's reversal does not resolve every question about the president's involvement. But it establishes that a Trump-appointed ambassador told Ukrainian officials that American military assistance was likely connected to the investigations the administration wanted announced.

For House investigators, the revised testimony adds another significant piece of evidence to an impeachment inquiry that continues to expand.