A former Ukrainian diplomat who alleges Kyiv meddled in the U.S. 2016 elections is set to begin sharing documents with three Senate committees, he told The Daily Beast.

The Intelligence Community and FBI Director Christopher Wray have pushed back against accusations of Ukrainian interference, and leading experts in the field say they are part of a “fictional narrative” pushed by the Kremlin. But three Senate chairmen are taking them seriously and investigating the claims nonetheless.

Telizhenko said he spoke last week by phone with staff working under Sens. Lindsey Graham (R-SC), Ron Johnson (R-WI), and Chuck Grassley (R-IA), and agreed to send documents to them in the coming days. After they’ve reviewed the materials, the GOP leaders will follow up about an in-person interview, Telizhenko said.

“It’s really professional,” he said. “They’re trying to understand what’s going on.”

Meanwhile, a spokesperson for Graham confirmed to The Daily Beast that the three chairmen are working on a joint investigation. That means their three committees–the Senate Judiciary Committee, the Senate Committee on Finance, and the Senate Homeland Security and Governmental Affairs Committee–have come together to investigate Ukraine’s alleged meddling in the 2016 election.

It’s a move that will frustrate national security, law enforcement and intelligence officials. Special Counsel Robert Mueller’s team secured indictments of 34 people while investigating the far-flung Russian campaign to destabilize America’s 2016 election; evidence for any Ukrainian counterpart, at this point, amounts to a few comments and an op-ed by a few Ukranian officials—plus Telizhenko’s allegations.

The Intelligence Community told Senators earlier this fall that Russian security services were pushing the allegations about Ukrainian meddling in 2016, according to The New York Times. For many members of Congress, that put the issue to bed; giving any legitimacy to Telizhenko’s allegations was akin to amplifying a Kremlin disinformation campaign. (“Thank God no one is accusing us of interfering in the U.S. elections anymore,” Vladimir Putin, the Russian president, said last month. “Now they’re accusing Ukraine.”)

But the matter remains front of mind for the White House, and Trump urged Ukrainian President Volodymyr Zelensky to investigate it in the July 25 phone call that led to his now-imminent impeachment. And as House Democrats assembled a multi-committee probe to scrutinize Trump’s pressure on Ukraine, their Senate Republican colleagues ramped up a parallel effort investigating Ukraine. Grassley’s queries about Ukraine and 2016 started in 2017, and long predate the impeachment inquiry.

Telizhenko’s plan to share materials with the Senate committees signals an important moment for both him and the three senators. There is no public evidence that any other U.S. government entities have reached out to Telizhenko about his claims. And over the last several months, Grassley, Graham, and Johnson have sent out a battery of document and information requests involving the Ukraine situation. They have asked for documents and information from the Department of Justice, the State Department, and the National Archives. But thus far, the government agencies in question have yet to share materials, a Grassley spokesperson told The Daily Beast. “We’ve been in contact with the recipients of the letters and are working with them to get responses,” a spokesperson for Johnson added.

Secretary of State Mike Pompeo has yet to respond to a letter Graham sent him on Nov. 21, according to a spokesperson for the Judiciary Committee. Despite a Dec. 5 deadline, the National Archives has yet to produce the documents about White House meetings during the Obama administration that Johnson and Grassley requested. And Attorney General Bill Barr has yet to fork over documents. A Justice Department spokesperson declined to comment, State Department spokespersons did not respond to requests for comment, and an Archives spokesperson said that the request “is still being processed in accordance with the Presidential Records Act.”

It’s not unusual for federal agencies to miss congressional deadlines. And when they do, it creates a dilemma for Hill investigators: They can send additional, more firmly worded letters; they can issue subpoenas; or they can give up. And while stand-offs between the executive and legislative branches often get testiest when the two are controlled by different parties, there can still be plenty of intra-party drama. Earlier in the Trump administration, a cadre of House Republicans went to war on the Justice Department as part of their scrutiny of the genesis of the Russia probe. Some even threatened to impeach then-Deputy Attorney General Rod Rosenstein, one of Trump’s political appointees.

It remains to be seen if there will be any sort of showdown between Barr and the three Republican Senate chairmen, all of whom are committed allies of the president.

Their probe is the latest project from Republicans eyeing Alexandra Chalupa, a Ukrainian-American who communicated with Ukrainian embassy officials during the 2016 election. Telizhenko alleges that his bosses at the embassy in Washington—where he worked at the time—directed him to send Chalupa any dirt he could find on Trump’s then-campaign chairman. Chalupa has said there was zero wrongdoing, and declined to comment for this story. Telizhenko’s accusations have found great purchase with Trump’s conservative allies, and he has been featured on One America News and Glenn Beck’s podcast. Fox News’ Sean Hannity has also highlighted his allegations, earning a Trump tweet.

Before Republicans and American media scrutinized Ukraine and 2016, the Russian Foreign Ministry alleged that Kyiv targeted Trump’s campaign. And after Politico reported Telizhenko’s allegations, Russian state media amplified the claims. Conspiracy site InfoWars also pushed the narrative. And a year and a half before he became acting attorney general, Matthew Whitaker filed a complaint with the Federal Election Commission about Chalupa. At the time, he helmed a conservative nonprofit called the Foundation for Accountability and Civic Trust, and touted the effort in an op-ed for The Hill.

Telizhenko went on to meet Republican power brokers, including Rep. Devin Nunes. And he has built a relationship with Trump’s personal lawyer Rudy Giuliani, accompanying him during his recent trip to Kyiv where he searched for damaging information on former Vice President Joe Biden and his son Hunter.

Giuliani’s months-long quest for Biden dirt is a key focus of Democrats’ impeachment inquiry. The House of Representatives is expected to vote on Wednesday on articles of impeachment.