Sen. Ron Johnson (R-Wis.) has issued the first subpoena of his Senate probe into the origins of special counsel Robert Mueller”;s investigation: to FBI Director Christopher Wray.

The subpoena, which POLITICO reviewed, demands documents but not testimony. Specifically, it asks for “;all documents related to the Crossfire Hurricane investigation”; –; the FBI”;s counterintelligence probe into Russian interference in the 2016 U.S. election. That probe scrutinized Americans close to then-candidate Donald Trump for their links to Kremlin officials. Mueller took over the probe in May 2017.

It”;s an unusual move, given that the president appointed Wray to his post helming the FBI. In the two years since Wray took that role, he has positioned himself as a low-profile defender of the institution –; often drawing ire from the president”;s allies in conservative media and on Capitol Hill.

Johnson also released a lengthy letter detailing the origins of his probe and criticizing the reaction it has garnered from media reports and Democrats. Democrats, Johnson wrote, “;have initiated a coordinated disinformation campaign and effort to personally attack”; himself and Finance Chairman Sen. Chuck Grassley (R-Iowa), whose office he has worked with.

The letter specifically addresses a recent Washington Post op-ed from Sen. Richard Blumenthal (D-Conn.). In the op-ed, Blumenthal said Johnson”;s investigation risked turning Congress into “;a forum for debunked conspiracy theories peddled by Kremlin proxies.”; Blumenthal cited a Post story reporting that a Ukrainian parliamentarian whose father worked in Russian intelligence said he”;d sent materials to Johnson”;s committee.

In his letter, Johnson reiterated that his committee has not received anything from that parliamentarian, Andriy Derkach. The U.S. Office of the Director of National Intelligence released a statement late last week saying that Derkach was participating in a Kremlin-backed effort to damage former vice president Joe Biden”;s presidential campaign.

“;It is neither me, Chairman Grassley, nor our committees that are being used to disseminate Russian disinformation,”; Johnson wrote. “;Instead, it is Democrats and the media that have been doing Russian President Vladimir Putin”;s work for him. Puppet masters in the Kremlin could not be more pleased at the political division and discord that has been driven by the resistance movement against President Trump.”;

Read more: politico.com