Washington (CNN) President Donald Trump's impeachment defense is being stripped away plank by plank by some of the administration officials caught up in his scheme to pressure Ukraine for political favors.

In testimony released by impeachment investigators, the US ambassador to the European Union also testified that he assumed it would be "illegal" for Trump's fixer and personal attorney Rudy Giuliani to push Ukraine to investigate the President's political opponents.

Sondland's adjusted testimony did much to dismantle the President's core and repeated defense: that he did not hold up aid to Kiev to force it to open a probe into Joe Biden and that any suggestion to the contrary is simply the "crazed" delusion of "Never Trumpers."

But his deposition was still punctuated by admissions that he could not remember what happened or did not know the motivations of key players -- signs of a potential attempt to protect the President.

Yet given the ossified political partisanship in the Congress, there were also signs that no disclosures, however damaging to the President, are likely to turn a party in thrall to his faithful political base against him and lead it to contemplate ejecting him from office.

Still, Sondland was not the only senior diplomatic figure to contradict the President's version of events on the second day of releases that threaten to turn into slow moving political torture for the White House.

The former US envoy to Ukraine, Kurt Volker, threatened another pillar of Trump's defense -- that the July 25 call with the Ukrainian President that Trump has said was "perfect" was in fact a "surprise" and "extremely unfortunate."

Tuesday's developments were a critical twist in an investigation that is on the cusp of a new and public phase that could further imperil the President and his 2020 election plans.

The disclosures appeared to significantly weaken the White House case that there was no quid pro quo with Ukraine and therefore no abuse of presidential power worthy of impeachment.

'A very grave development'

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Democrats immediately seized on Tuesday's events to argue that a devastating hole had been blown in Trump's defense.

"This is a very grave development for both Ambassador Sondland and frankly for President Trump and his Republican defenders," Virginia Rep. Gerry Connolly told CNN's Wolf Blitzer.

"The entire defense by President Trump and his Republican acolytes in Congress that there was no quid pro quo has now collapsed."

A growing list of witnesses, including the top diplomat in Ukraine William Taylor and National Security Council aide Tim Morrison, have testified that Ukraine opening political probes was linked to $400 million in aid and a potential meeting between Trump and Ukrainian President Volodymyr Zelensky.

Further damaging revelations are possible in the coming days as Democrats preside over the release of testimony taken behind closed doors as they prepare for public impeachment hearings.

The evidence from Sondland and Volker was far from the only damaging development over the last few days for Trump and his loyal troops on Capitol Hill.

Growing evidence, meanwhile, of a shadow foreign policy scheme masterminded by Giuliani and stretching over months undermines Trump's focus on two events -- the call with Zelensky and a whistleblower report -- as the only significant data points in the scandal.

At one point, Sondland deepened the political plight of Secretary of State Mike Pompeo, who appears to have been aware of the Giuliani scheme but did nothing to stop it: "Pompeo rolled his eyes and said: 'Yes, it's something we have to deal with.' "

The White House responded to Tuesday's events in characteristic fashion, with press secretary Stephanie Grisham ignoring the existence of newly disclosed facts.

"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," she said.

But Grisham also seized on Volker's statement that he was not aware of the existence of a quid pro quo and belief that the new Kiev government did not know aid was held up. She also pointed out that Sondland did not directly tie Trump personally to the demand for a quid pro quo.

"Both transcripts released today show there is even less evidence for this illegitimate impeachment sham than previously thought," she said in a statement.

Grisham's commentary was undermined by Sondland's new testimony itself since he now says he told a Zelensky aide that the security assistance an announcement of a public investigation were in fact linked.

McConnell stands firm

Sen. Chris Coons, D-Delaware, said on CNN's "The Situation Room" that Sondland's profile made his revised testimony even more significant and damaging to the President.

"This is not some anonymous whistleblower. This cannot be argued to be some action by a deep state opponent of President Trump," Coons said. "Gordon Sondland, the ambassador to the EU, was a major Republican donor and a supporter of President Trump."

Tuesday's disclosures seemed to wound Trump in the fact-based environment of an impeachment probe, but his political future is playing out in front of diverse audiences. While Democrats see further proof of guilt, Republican lawmakers seem likely to simply fall back on a new set of arguments.

They can make the somewhat implausible case that since Sondland did not implicate the President in the quid pro quo, he could have been acting on his own initiative or the orders of someone else.

They can try to repurpose the argument that a quid pro quo is not illegal and a fact of foreign policy -- a point made last month by White House acting chief of staff Mick Mulvaney that was quickly withdrawn.

Or they can reach a last resort position that Trump's conduct may not be acceptable but is not impeachable -- however much that might anger a President who insists he did nothing wrong.

Whatever they say, Tuesday's developments, while changing the legal and logical context of the impeachment inquiry are unlikely to shift the locked in political dynamics imposed by America's tribal partisan environment.

"I'm pretty sure how it's likely to end. If it were today, I don't think there's any question it would not lead to removal," GOP Senate Majority Leader Mitch McConnell said Tuesday, speaking about the prospects for an impeachment trial in the Republican-led Senate.

That doesn't mean Republicans aren't sweating. A source close to the White House who speaks to Trump regularly offered a grim assessment to CNN's Jim Acosta of the aftermath of Tuesday night's races in Virginia and Kentucky, where Democrats made solid gains.

"Totally bad. Kentucky and Virginia signal to GOP they are underestimating voter intensity against Trump, and it could be terrible for them next year," the source said.

"Bad omen for impeachment," the source added.

But the wider politics of impeachment are still tough to call. No revelations, however damning, are likely to shake Trump's hold on his political base glued together by his claim, last made in Kentucky Monday night, that the Democratic tactics are the "crazed" actions of a party seeking to overturn an election.

And new polls show that in the swing states that will decide whether he wins a second term, public opinion is closely divided on whether he should be impeached and removed from office.

But Sondland's testimony offered a preview of how damaging testimony by witnesses close to the President could undermine his narrative on Ukraine and wrongdoing. That could have the potential to reshape wider public opinion among more moderate voters Trump also needs a year from now.