WASHINGTON — President Donald Trump and his allies were left scrambling Wednesday morning after impeachment inquiry testimony by the U.S. ambassador to the European Union, Gordon Sondland, dealt a blow to the argument at the heart of the White House's defense.

Sondland allegedthat a White House visit by Ukraine's president had indeed been linked to the announcement of political investigations into Trump political rival Joe Biden and his son, an apparent contradiction of Sondland's assessment in an earlier closed-door deposition the White House has repeatedly cited.

The claim sent the president’s defenders racing to revise talking points that have depended on a “no quid pro quo” defense, said Trump allies outside the White House, delivering a significant setback to Republican pushback.

Trump himself seized on Sondland's recollection of a September phone conversation between the two men, re-enacting the conversation for reporters on the South Lawn of the White House Wednesday as the hearing continued. "I want nothing. I want nothing. I want no quid pro quo. Tell Zelenskiy to do the right thing," the president said he told the ambassador then.

“I WANT NOTHING. I WANT NOTHING. I WANT NO QUID PRO QUO,” read hand-written notes Trump carried in his hands on White House stationery during his comments.

President Donald Trump holds notes on Ambassador Gordon Sondland's testimony as he departs the White House on Nov. 20, 2019. Erin Scott / Reuters

After reading the brief handwritten statement, the president did not take questions from reporters as he left the White House nearly an hour later than scheduled for a tour of an Apple plant in Texas.

Later, he said on Twitter that the Sondland testimony had exonerated him. "Impeachment Witch Hunt is now OVER!" he wrote, again recounting the alleged July conversation between himself and his E.U. ambassador, writing that he had told Sondland: ”I WANT NOTHING! I WANT NOTHING! I WANT NO QUID PRO QUO! TELL PRESIDENT ZELENSKY TO DO THE RIGHT THING!”

In the past, the president has offered praise for Sondland, on multiple occasions holding up elements of his closed-door deposition to undercut Democrats’ impeachment inquiry.

Download the NBC News app for breaking news and politics

“The ambassador — who I heard was tremendous, and a tremendous person — he was 100 percent for what we're saying," Trump said of Sondland on Oct. 4. "A hundred percent. And, if you look, he also said there was no quid pro quo. That's the whole ballgame.”

On Wednesday, as Trump recounted their July conversation, he emphasized the distance between them, saying that Sondland had first backed other presidential candidates. "I don't know him very well. I have not spoken to him much. This is not a man I know well. Seems like a nice guy, though. But I don't know him well," Trump told reporters.

But while Trump’s defenders have sought to undercut other witnesses, saying they were “never Trumpers” or part of a “deep state” conspiracy, that was not an argument that stood to be used effectively against Sondland — a former hotelier who donated $1 million to the president’s inaugural committee in 2017, according to an outside campaign adviser.

The president's re-election campaign was slower than usual to respond to Sondland’s opening statement. Some of the Republican Twitter accounts that typically have pre-written talking points and graphics ready for release as a messaging strategy stayed focused instead on Sondland’s closed-door deposition, rather than the first part of Wednesday’s public hearing.

The White House and its defenders began to pivot their argument later in the morning, with the Trump campaign noting that the president had raised the idea of a White House visit for the Ukrainian president in a letter and two phone calls, though a precise date was never agreed on and formal arrangements were never made.

They also characterized Sondland’s Wednesday testimony as being based on "presumptions" he had made regarding Trump’s reasoning for withholding aid, according to people close to and familiar with the White House strategy, citing Sondland's statement that he had never heard Trump explicitly state that aid was linked to the investigations, though he conveyed that message to the Ukrainians.

The Sondland testimony highlighted again the White House's struggle to mount a sustained messaging response to the impeachment inquiry. Former Florida Attorney General Pam Bondi, recently hired by the White House to manage impeachment communications strategy, repeatedly called Sondland the ambassador to Ukraine rather than the European Union and did not deliver a clear message on the extent of his relationship with Trump in an interview Wednesday on "CBS This Morning."

"The president knows him. The president does not know him very well," Bondi said. "He's a short-term ambassador. Of course he knows him. He's the ambassador."

White House officials soon echoed Trump in looking to focus attention on the July conversation between the president and Sondland. “Ambassador Sondland’s testimony made clear that in one of the few brief phone calls he had with President Trump, the president clearly stated that he ‘wanted nothing’ from Ukraine and repeated ‘no quid pro quo' over and over again," White House press secretary Stephanie Grisham said in a statement.

A campaign spokesman downplayed 2020 team concerns over Sondland's testimony. “He testified previously that the president expressly said he wasn’t asking for a quid pro quo. He hasn’t contradicted that and in fact his testimony is consistent with that,” said Tim Murtaugh.

Still, Trump’s television defenders acknowledged it wasn’t a good day for him.

“It doesn’t look good for the president, substantively,” Ken Starr, who led the investigation into President Bill Clinton's affair with Monica Lewinsky, said on Fox News.