The White House changed course on Thursday when President Donald Trump's acting chief of staff told reporters that yes, there had been a quid pro quo involved in delaying military aid to Ukraine. Then he sharply backtracked.

The arrangement didn't have anything to do with Trump's request that Ukrainian President Volodymyr Zelensky look into 2020 rival Joe Biden. Rather, Mick Mulvaney told reporters the delay in aid was tied to a Trump administration theory that Ukraine was involved in hacking the Democratic National Committee's servers in 2016.

Mulvaney reversed those statements later in the day, claiming the media spun his words and that the president never asked him to tie the aid money to the investigation of the server.

Republicans who support Trump have all echoed a similar refrain: There was no quid pro quo. But that message evolved from vehement denial, to embracing the help of foreign countries in rooting out corruption, to yesterday: Bargaining with aid in exchange for an investigation into domestic politics is normal.

The allegation that Trump pressured Zelensky to dig up dirt on the former vice president in exchange for releasing $400 million already approved by Congress stems from an anonymous whistleblower complaint that prompted House Democrats to conduct an impeachment inquiry into the president.

The whistleblower said officials were concerned Trump "is using the power of his office to solicit interference from a foreign country in the 2020 U.S. election." In a summary put out by the White House of a July 25 call, Trump asked Zelensky to "look into" Joe and Hunter Biden.

Trump has pushed the claim, without any credible evidence, that the former vice president pressured Ukraine to fire a prosecutor to help his son, who at one time on the board of a Ukrainian energy company.

Explainer:What really happened when Biden and the U.S. forced out Ukraine's top prosecutor

Democrats said if Trump dangled that aid in front of Zelensky in exchange for help in the 2020 election, it would be serious misconduct.

Trump called it a "perfect call" with Zelensky. But critics have honed in on this line from the partial transcript: "I would like you to do us a favor though," Trump said.

That request came after Zelensky indicated Ukraine wanted to purchase military equipment. Trump went on to ask Zelensky to look into details a hacking of the DNC prior to the 2016 election that was linked back to Russia.

Read:The summary of President Trump's call with Ukraine president about Biden, as released by the White House

First, Trump and his allies maintained for weeks that there was zero quid pro quo to be found in the call.

“I’ve read the transcript in its entirety. It shows that there was no quid pro quo," said Sen. Chuck Grassley, R-Iowa, after the White House's summary was released. "The Ukrainian president admitted problems with corruption in the country and agreed that the issue at hand warranted looking into further."

“What a nothing (non-quid pro quo) burger,” tweeted Sen. Lindsey Graham, R-S.C. “Democrats have lost their minds when it comes to President @realDonaldTrump.”

Democrats, meanwhile, said there was corruption, whether the pressure was explicit or implicit that Ukraine should cooperate in exchange for aid.

Initial responses:GOP dismisses Trump's Ukraine call as Democrats compare it to a 'mob shakedown'

But as more details were released from closed-door testimony of Trump administration officials before Congress, the "no quid pro quo" defense seemed to weaken.

Text messages released by House Democrats show diplomats discussing the issue of quid pro quo. William Taylor, a U.S. diplomat in Ukraine, said it was “crazy to withhold security assistance” to Ukraine in exchange for “help with a political campaign.”

Ambassador to the European Union Gordon Sondland responded that the assertion was “incorrect” about Trump’s intentions. “The President has been crystal clear no quid pro quo’s of any kind,” Sondland said.

More texts:A visual timeline of the text messages in the Trump-Ukraine affair

Trump then added China into the mix when he said that the trade rival should also look into the Bidens, days before he was set to negotiate a trade deal with Chinese officials.

He said on Twitter that he has "an absolute right, perhaps even a duty, to investigate, or have investigated, CORRUPTION, and that would include asking, or suggesting, other Countries to help us out!"

And Mulvaney's initial comments Thursday indicate that even if there was a quid pro quo, it's a normal, acceptable course of business for a U.S. president.

"This is a corrupt place. Everybody knows this is a corrupt place," Mulvaney said of Ukraine at the press conference. He was responding to the question: Why did the administration delay the military aid that was apportioned for Ukraine?

"As vocal as the Europeans are about supporting Ukraine, they are really, really stingy when it comes to lethal aid," Mulvaney added, repeating Trump's complaint that the U.S. was spending more on Ukraine aid than other nations.

"Did he also mention to me in the past the corruption related to the DNC server? Absolutely," Mulvaney said. "No question about that, but that's it and that's why we held up the money."

Trump has floated the theory that the DNC server and emails from Hillary Clinton "could be" in Ukraine. That's been debunked, and is one piece of a conspiracy theory in which Ukraine, not Russia, meddled in the 2016 election.

Trump's claims:Conspiracy theories thrive in Ukraine, where a young democracy battles corruption

When asked to clarify, Mulvaney reiterated: "The look back to what happened in 2016 certainly was part of the thing that he was worried about in corruption with that nation, and that is absolutely appropriate."

"And withholding the funding?" ABC News' Jon Karl asked.

Mulvaney affirmed it again: "Yeah. Which ultimately then, flowed."

"Let's be clear. What you just described is a quid pro quo," Karl again pressed for clarity. "It is: Funding will not flow unless the investigation into the Democratic server happened as well."

Mulvaney said in response, "We do that all the time with foreign policy. ... I have news for everybody. Get over it. There's going to be political influence in foreign policy."

He accused Trump's critics of a witch hunt driven by disdain for Trump's policy, as opposed to concern over Trump's actions being for personal political gain.

The aid was finally permitted to be released to Ukraine last month.

"It doesn't get any clearer than that. 'We do that all the time. Get over it.This is what happens in politics.' He knew exactly what he was saying," Rep. Maxine Waters, D-Calif., said to CNN. "Mulvaney, you just outed the president of the United States."

Now, Mulvaney's attempt to walk his press conference comments back is a dig at the news media's framing. He said in a statement, "Once again, the media has decided to misconstrue my comments to advance a biased and political witch hunt against President Trump."

"There was never any condition on the flow of aid related to the matter of the DNC server," he added.

That answer doesn't satisfy many of Trump's adversaries, who have seized on the latest messaging coming out of the White House.

House Oversight Committee Chairman Adam Schiff said of Mulvaney's later walk-back of his comments, "I didn't find it the least bit credible."

As Democrats continue their probe, the question becomes whether this admission was of an impeachable offense, and whether it matters if a quid pro quo was in the mix at all.

Schiff said Thursday that Mulvaney’s acknowledgment of a quid pro quo "certainly indicates that things have gone from very very bad to much much worse."

As for the president's take, "I think he clarified it," Trump said on Friday of Mulvaney's statement.

Contributing: Kim Hjelmgaard, Ledyard King, Nicholas Wu, John Fritze, Christal Hayes