The Democratic allegations at the heart of the ongoing impeachment inquiry are pretty simple: that Donald Trump used the power of the presidency to pressure a foreign government to improperly investigate Joe Biden. Or as Democrat Eric Swalwell of California summarized it on Nov. 7, “Defense dollars for dirt.”

The Republican response, by contrast, has been less straightforward. In the weeks since Sept. 24, when the White House released a rough transcript of Trump’s July 25 call with Ukrainian president Volodomyr Zelensky, the Republican defense has shifted dramatically, from denying the charges and then dismissing that they would be impeachable if true, to denigrating witnesses and evidence and attacking the impeachment process.

Democrats paint the changing defense as evidence of its weakness. Republicans attribute it to another source: disorganization. So far, they say, there’s been little coordination between the White House and Trump’s nominal allies on the Hill about a messaging strategy.

But the GOP tried to institute some order before the first day of public testimony in the House’s impeachment hearings, circulating a memo from staff to Republican committee members the day before— which was obtained by TIME— outlining “four key pieces of evidence” that they believe are “fatal to the Democrats’ allegations.”

Here’s a look at how the defense of Donald Trump has changed since the impeachment proceedings began.

‘No Quid Pro Quo’

Since the moment he authorized the release of a transcript, Trump has maintained there was no quid pro quo in his withholding military aid from Ukraine while pushing the country to investigate Joe and Hunter Biden. In a tweet announcing the decision to publish the call, Trump said his conversation with President Zelensky was “totally appropriate,” that he applied “no pressure,” and that there was “NO quid pro quo.”

Trump has continued to chant this mantra at rallies, on Twitter and in interviews — a blanket defense of the core issue at the center of Democrats’ investigation. And it has been echoed by other top members of his Administration. “The transcript of the President’s phone call with President Zelensky… there was no quid pro quo,” Vice President Mike Pence said on Oct. 3. “There was no pressure.” Kellyanne Conway, counselor to the president, Larry Kudlow, Trump’s chief economic advisor, Steve Mnuchin, Treasury secretary, and others of Trump’s top allies have all repeated this line as well.

But this stance has become more complicated in recent days as witnesses have asserted explicitly to House investigators that there was, in fact, a quid pro quo.

“That was my clear understanding,” William Taylor, the top U.S. diplomat in Ukraine, testified last month. “Security assistance money would not come until the president [of Ukraine] committed to pursue the investigation,” Taylor continued, according to the transcript of his testimony. Taylor reaffirmed this in public testimony on Nov. 13. “[Gordon Sondland] described conditions for the security assistance and the White House meeting in those terms,” Taylor said. “That is, they were dependent upon— conditioned upon— pursuing these investigations.”

On Nov. 5, Sondland, the U.S. Ambassador to the European Union, revised his original testimony to include that he had passed along such a message to a Zelensky advisor. “I said that resumption of the U.S. aid would likely not occur until Ukraine provided the public anticorruption statement that we had been discussing for many weeks,” Sondland said in a written statement.

Some Trump aides adjusted their strategy, and been backing away from an unequivocal “no quid pro quo” defense.

On Nov. 3, for example, Conway changed her tune on CNN. She continued to say there was no quid pro quo, but then when pressed by CNN’s Dana Bash, Conway said, “I don’t know whether aid was being held up and for how long.”

Attacking the process

When Pelosi announced the start of a formal impeachment inquiry on Sept. 24, Republicans immediately began decrying the process and questioning the legitimacy of the investigation. In past impeachments, the inquiries had been voted on by the full House, whereas in this case, Pelosi didn’t hold a vote to begin it. While that broke with tradition, there is nothing in the Constitution that says the House needs a vote to begin an impeachment investigation. But Republicans and White House lawyers seized on the procedural omission to defend Trump nonetheless. As the investigation has proceeded, they’ve also criticized the fact that many of the hearings have been held behind closed doors.

“This is a process problem,” Rep. Mark Meadows, an ally of the President and leader of the Freedom Caucus, told TIME in late October. “If you focus on communication and not process, you’re focusing on the wrong thing.”

On Oct. 8, White House Counsel Pat Cipollone sent a letter to House Democratic leaders in which he said they “have designed and implemented your inquiry in a manner that violates fundamental fairness and constitutionally mandated due process,” specifically citing the lack of a House vote to authorize it. He announced that Trump and his Administration would not cooperate with the investigation.

“We think there’s serious constitutional flaws [with] the way the process is going on,” Trump’s personal attorney Jay Sekulow told TIME on Oct. 22.

Senate Judiciary Chairman Lindsey Graham introduced a resolution in October condemning the inquiry, arguing that Democrats are “abandoning more than a century’s worth of precedent and tradition in impeachment proceedings and denying President Trump basic fairness and due process accorded every American.” Graham and other Republicans have complained both about the lack of a full House vote to begin the probe and that the testimony has thus far largely not been public.

On Oct. 31, the House did vote on formalizing the inquiry, and public hearings are set to start next week. While he often refers to the impeachment investigation as a “witch hunt” — the same term he used to describe Robert Mueller’s investigation — Trump has urged Republicans to move away from process arguments as the inquiry has proceeded. “I’d rather go into the details of the case rather than process,” Trump told reporters on Oct. 28 of how Republicans in Congress were defending him. “Process is good, but I think you ought to look at the case, and the case is very simple and quick.”

Undermining the credibility of witnesses

Trump and his allies have attempted to undermine the credibility of certain witnesses and poke holes in their testimony. Trump has repeatedly attacked the whistleblower whose complaint spurred the impeachment inquiry, calling for the person’s identity to be revealed and criticizing the media for not publishing it. He has also asserted, without evidence, that the whistleblower has a political agenda.

“There have have been stories written about a certain individual, a male, and they say he’s the whistleblower,” Trump told reporters on Nov. 3. “If he’s the whistleblower, he has no credibility because he’s a Brennan guy, he’s a Susan Rice guy, he’s an Obama guy. And he hates Trump.”

After Lt. Col. Alexander Vindman, a National Security Council official, testified behind closed doors on Oct. 29, Trump tweeted that he was a “Never Trumper witness.” On Nov. 2, when asked whether he regrets that comment, Trump seemed to imply he had damaging information to release about Vindman: “Well, you’ll be seeing very soon what comes out and then you can ask the question in a different way,” Trump said.

As members of conservative media amplified Trump’s attacks on Vindman, who was born in Ukraine, and questioned his patriotism, some Republicans in Congress condemned the line of attack. “I’m not going to question the patriotism of any of the people who are coming forward,” Senate Majority Leader Mitch McConnell said the day of Vindman’s testimony. House Republican Conference Chairwoman Liz Cheney said questioning Vindman’s patriotism was “shameful.”

Sondland, on the other hand, is a Trump donor, and can’t be criticized as a “Never Trumper.” When he updated his testimony in a statement that said he had been the messenger of a quid pro quo, White House press secretary Stephanie Grisham released a statement saying, in part, “Ambassador Sondland squarely states that he ‘did not know, (and still does not know) when, why or by whom the aid was suspended.’ He also said he ‘presumed’ there was a link to the aid — but cannot identify any solid source for that assumption.”

There may have been a quid pro quo, but that’s not impeachable

On Oct. 17, acting White House chief of staff Mick Mulvaney held a press conference in which he dramatically changed the defense of Trump’s actions, and then walked back his comments hours later. While Trump had been continuing to proclaim “no quid pro quo,” while standing behind the podium in the White House press briefing room, Mulvaney seemed to acknowledge that there had been one — but that it wasn’t a problem. “Did he also mention to me in [the] past the corruption related to the DNC server? Absolutely,” Mulvaney said of a conversation he had with Trump. “No question about that. But that’s it, and that’s why we held up the money.”

“I have news for everybody: Get over it,” Mulvaney said. “There’s going to be political influence in foreign policy.”

Reaction to what seemed to be the first acknowledgement of a quid pro quo in the conversation at the heart of the impeachment inquiry was swift, and hours later, Mulvaney put out a statement disputing his earlier comments. “There was absolutely no quid pro quo between Ukrainian military aid and any investigation into the 2016 election,” he said in his later statement.

While he had to walk back his explanation of why Trump held up aid money to Ukraine, others are now shifting to a defense of Trump that mirrors Mulvaney’s original comments: that there may have been a quid pro quo, but that’s not an impeachable offense.

This line of defense has emerged as multiple witnesses (including Sondland and Taylor) have testified about the occurrence of a quid pro quo. “If it was a condition of getting aid that there be an investigation into a political rival, that was inappropriate,” the top Republican on the House Armed Services Committee, Mac Thornberry of Texas, told NPR on Oct. 28. “Whether it rises to the standard of being an impeachable offense — that’s a different question.”

“The Senate will face the question of whether that’s an impeachable offense,” Sen. Roger Wicker, a Republican from Mississippi, told CNN in November. “And I don’t think the American people are going to conclude that it is.”

Trump is no fan of this tactic, however, as he still maintains that there was no quid pro quo at the base of the matter. “False stories are being reported that a few Republican Senators are saying that President Trump may have done a quid pro quo, but it doesn’t matter, there is nothing wrong with that, it is not an impeachable event,” the President tweeted on Nov. 4. “Perhaps so, but read the transcript, there is no quid pro quo!”

Ukraine is out to get Trump

Trump has maintained that his interest in Ukraine had to do with rooting out corruption in the country, and has espoused a conspiracy theory that the nation colluded with Hillary Clinton in 2016 by by hiding the Democratic National Committee’s email server and disseminating dirt about Trump. “He’s always looking for corruption, which is what more people should be doing,” Trump said in response to a question from TIME on Oct. 28 about his lawyer Rudy Giuliani, who Trump invoked on the July 25 call with Zelensky.

Read more: How Trump’s Obsession With a Conspiracy Theory Led to the Impeachment Crisis

The memo and questioning by the Intelligence Committee Republican counsel Steve Castor during public testimony on Nov. 13 pushed this idea that Trump is justified in his worries about Ukraine and that the country has worked to oppose him.

While questioning witnesses George Kent and Taylor, Castor referred to “elements of the Ukrainian establishment that were out to get the president,” and tried to get Taylor to agree that is a “reasonable” thing for Trump to believe.

“President Trump’s concerns about Ukraine’s role in the 2016 election. You believe he genuinely believed they were working against him, right?” Castor asked. Taylor responded he did not know.

The memo circulated the previous day encouraged Republican members to highlight Trump’s “deep-seated, genuine, and reasonable skepticism about Ukraine due to its history of pervasive corruption” and claims that “senior Ukrainian government officials interfered in the 2016 U.S. presidential election in opposition to President Trump.”

This line of argument works to add a justification for Trump’s interest in Ukraine and minimize the idea that he was simply looking for his own political benefit from the suggested investigations.

Public hearings: All of the above

Republicans prepared and previewed their main points before the first public hearings in the impeachment probe on Nov. 13 in a memo that had been sent around the previous day. This memo urged the Republican questioners to focus on four points that could undermine the idea that Trump engaged in an impeachable offense: the July 25 call summary “shows no conditionality or evidence of pressure,” both Trump and Zelensky have said there was no pressure on the call, the Ukrainian government was not aware that the security assistance had been held up at the time of the July 25 call, and the two presidents met and aid was resumed in September without an announcement that Ukraine would investigate the Bidens, according to the memo.

The substance of this memo is evidently aimed to bolster the original “no quid pro quo” defense, by establishing that there was no pressure on Ukraine to investigate the Bidens and that the delayed assistance was not conditioned upon that.

During his time to speak before witnesses Kent and Taylor, Rep. Devin Nunes of California, the ranking member of the committee, ticked through the basic ideas outlined in the memo. “We’re supposed to believe that President Trump committed a terrible crime that never actually occurred, and which the supposed victim denies ever happened,” he said. Rep. Jim Jordan of Ohio questioned Taylor about three meetings he attended with Zelensky during which the Ukrainian president did not mention the investigations that Taylor understood to be linked to the security assistance. Rep. John Ratcliffe of Texas read numerous quotes by Zelensky saying he didn’t feel pressure from Trump. “The Ukrainian President stood in front of the world press and repeatedly, consistently, over and over again, interview after interview, said he had no knowledge of military aid being withheld,” Ratcliffe said. “Meaning no quid pro quo, no pressure, no demands, no threats, no blackmail. Nothing corrupt.”

Rep. Elise Stefanik of New York succinctly summarized the main elements of the GOP defense: “For the millions of Americans viewing today, the two most important facts are the following,” she said. “Number one: Ukraine received the aid. Number two: there was in fact no investigation into Biden.”

But not all of the Republicans on the committee stuck to the key points from the memo, and some continued with previous lines of defense. During his opening statement, Nunes also continued criticizing the process of the impeachment inquiry and calling into question the credibility of the whistleblower and witnesses. During his opening statement, Nunes called the impeachment investigation a “horrifically one-sided process” and said it is “an impeachment process in search of a crime.” He also claimed the whistleblower has “a bias against President Trump,” and dismissed “officials’ alarm at the President’s actions” as “typically based on second-hand, third-hand, and even fourth-hand rumors and innuendo.”

Rep. Mike Turner of Ohio used all of his questioning to highlight out that neither Kent nor Taylor has ever had direct contact with Trump, attempting to diminish their value as witnesses. “The man that neither one of you have had any contact with, you’re the first up witnesses,” Turner said. “I just find that a little amazing.”

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Write to Tessa Berenson at tessa.berenson@time.com.