Among the 100 U.S. senators who could decide President Trump’s fate in an impeachment trial, only one of them can claim to be a fact witness to the allegations at hand as much as they can claim to be a juror: Sen. Ron Johnson.

The two-term Wisconsin Republican chairs the Senate Foreign Relations Committee’s panel on Europe, and as part of that role, he has been as engaged as anyone in Congress on matters involving Ukraine. As a result, he has become a go-to lawmaker for the White House for the region.

But in the issues at the heart of the House of Representatives’ impeachment inquiry, Johnson has played an even more outsized role than his jurisdiction entails. The senator has been an inescapable presence in the Ukraine saga: Not only has he been present for several key events in the timeline of Trumpworld’s apparent push to get Ukraine to investigate the Bidens, Johnson has also had personal conversations with many of the major figures involved, from Trump to Ukrainian President Volodymyr Zelensky to U.S. Ambassador to the E.U. Gordon Sondland.

On the back-and-forth between Washington and Kyiv, Johnson is considered so plugged-in—at least by his Republican colleagues—that they have called on him to share what he knows for the purposes of the inquiry. On Monday, Reps. Jim Jordan (R-OH) and Devin Nunes (R-CA), two of the GOP’s lead impeachment critics, wrote to Johnson asking him to offer his recollection of events; he did so that afternoon in a lengthy letter in which he detailed several meetings with Ukrainian and U.S. officials, trips to Ukraine, and private conversations with Trump himself.

“ The people that elected me certainly deserve representation in this process. I don’t think there’s any kind of conflict there whatsoever. I think every senator has some input or some bias in this thing, anyway, so you start disqualifying everyone if you disqualify on that basis. ” — Sen. Ron Johnson (R-WI)

However, Johnson has rejected any suggestion that his role in the Ukraine drama means he should recuse himself from an impeachment trial—and forcefully pushed back on the idea that his deep involvement presents any kind of conflict.

“The people that elected me certainly deserve representation in this process,” Johnson told reporters on Monday evening. “I don’t think there’s any kind of conflict there whatsoever. I think every senator has some input or some bias in this thing, anyway, so you start disqualifying everyone if you disqualify on that basis.”

Johnson’s insistence sets up what could be a remarkable role for a U.S. senator in an impeachment proceeding and perhaps a defining moment in the Wisconsin senator’s political career.

His case is “unique and somewhat peculiar,” said Gregg Nunziata, a former GOP staffer on the Senate Judiciary Committee.

“It just underscores the limits to which we can treat the impeachment process anything like a typical trial,” he told The Daily Beast. “A trial of a political matter before the Senate is not a trial before an impartial jury… Johnson’s just an extreme example.”

While many GOP colleagues maintain silence on Ukraine, with some justifying that silence with the fact they could later be jurors in an impeachment trial, Johnson occupies an almost entirely different plane. The senator—a staunchly conservative ally of the president who has used his perch as chair of the Senate’s government oversight panel to investigate Hillary Clinton’s emails—was early to dive into far-fetched theories suggesting that Ukraine had meaningfully intervened in the 2016 election in order to help Clinton defeat Trump.

In particular, Johnson has closely followed the reporting of John Solomon—the journalist who wrote columns for the Hill newspaper that were fed by Ukrainian officials such as former prosecutor Yuriy Lutsenko, a man who U.S. officials have testified peddled questionable information in order to serve his own interests. The narrative that Ukrainian officials were out to get Trump was pushed so aggressively, that the president raised the theories directly to Zelensky during their July 25 phone call.

Even before the anonymous whistleblower came forward to describe that call in a formal complaint, Johnson was touting Solomon’s work. After returning from a visit to Kyiv over Labor Day with Sen. Chris Murphy (D-CT), Johnson was asked by reporters on Sept. 10 about Rudy Giuliani’s then-publicly known push for Ukraine to investigate the Bidens.

“I don't think there's a need for further investigation out of Ukraine, anyway,” said Johnson. “I mean, the investigation here is going to shift in the U.S. Just read anything by John Solomon, who’s probably doing most of the groundwork on this. Take a look at what he’s been doing and what he’s gonna be coming up with.”

Johnson has continued to reference Solomon’s reporting despite weeks of public scrutiny. On Nov. 6, the senator spoke to reporters off the Senate floor and directed them to Solomon’s lawsuit to release communications between the State Department and entities associated with Hunter Biden and Burisma, the Ukrainian gas company on whose board Biden served. Johnson said the query could reveal that Barack Obama’s administration was aware of possible conflicts within the Biden family.

“I'm just trying to tenaciously gather information so we can, at some point in time, determine the truth,” said Johnson.

Johnson’s belief in Ukrainian election meddling—and general Clinton wrongdoing—animate his lengthy response letter to the GOP lawmakers who requested an account from him on Ukraine. In fact, Johnson writes that his “first-hand knowledge and involvement in this saga began with the revelation that… Clinton kept a private email server.”

“I view this impeachment inquiry as a continuation of a concerted, and possibly coordinated, effort to sabotage the Trump administration that probably began in earnest the day after the 2016 presidential election,” Johnson wrote to Nunes and Jordan, both of whom share a similar worldview.

“ It just underscores the limits to which we can treat the impeachment process anything like a typical trial. A trial of a political matter before the Senate is not a trial before an impartial jury… Johnson’s just an extreme example. ” — Gregg Nunziata, a former GOP staffer on the Senate Judiciary Committee.

That letter also reveals just how embedded the senator is in the Ukraine timeline. Johnson recalls a series of events dating back to May 2019 in which he was personally involved, including a White House visit, a lengthy phone call with Trump, and two visits to Ukraine. In his telling, Trump had legitimate concerns about Ukrainian corruption and was largely unaware of the machinations of officials like Sondland about “investigations,” suggesting they were possibly acting on their own volition, not on Trump’s orders. Johnson notably told the Wall Street Journal in October that he had learned about a possible quid pro quo from Sondland and “winced” at the idea.

At points, Johnson’s version of events does not match what was offered in sworn testimony from witnesses deposed in the impeachment inquiry. For example, Johnson notes he doesn’t recall, as Sondland testified, that Trump directed a group of officials to work with Giuliani on Ukraine matters. “I have no recollection of the president saying that during the meeting. It is entirely possible he did, but because I do not work for the president, if made, that comment simply did not register with me. I also remember Sondland staying behind to talk to the president as the rest of the delegation left the Oval Office.”

Johnson’s letter also shows him playing another role. Despite his own concerns about Ukraine, he was a strong supporter of the security aid going through to the new Zelensky government. The senator personally assuaged Ukrainian officials of their concerns about Trump’s attitudes and the tied-up security aid, and positioned himself as a conduit between them and Washington. “I explained that I had tried to persuade the president to authorize me to announce the hold was released but that I was unsuccessful,” Johnson writes of his September meeting with Zelensky.

Some House Democrats involved in the inquiry were reluctant to say much about what Johnson’s role in any impeachment proceeding should be, deferring to the Senate. But those who read his Monday letter had strong feelings about it.

“It’s just disgusting,” said Rep. Jim Himes (D-CT), a member of the House Intelligence Committee said of Johnson’s letter, which he framed as another GOP attempt to undermine the substance of the impeachment inquiry. “I’ve been doing this for a little while. I don’t see anybody on that side acting in good faith. They’re doing bullshit tricks, like forcing [House Intelligence Committee Chair] Adam [Schiff] to gavel down [Rep. Elise] Stefanik so they can generate a Fox News headline.”

A House Democratic aide said the letter is actually helpful to their side’s case. “Even this lame attempt to spin us is harmful to their case,” the aide said, adding that “the fact it’s not under oath means it’s meaningless.”

But Johnson, looking at the other side of the Capitol at an inquiry that may wrap him even further into a drama that is rattling the core of U.S. government, is adamant that nothing he witnessed over the course of the last seven months comes close to being an impeachable offense.

“I don't know what the House is trying to do here,” Johnson told the Milwaukee Journal Sentinel last week. “In the end, I think this is, unfortunately, a very sad farce on the part of the House.”