U.S. Sen. Richard Blumenthal, D-Connecticut, joined two other Democrats Monday in taking legal action to challenge the constitutionality of President Donald Trump‘s decision to appoint Matthew Whitaker acting attorney general.

Blumenthal and U.S. Sens. Sheldon Whitehouse, D-Rhode Island, and Mazie Hirono, D-Hawaii, filed a complaint in the U.S. District Court for the District of Columbia alleging that the president violated the Constitution’s Appointments Clause by selecting Whitaker, who has never been confirmed by the Senate.

The effort, supported by Protect Democracy and the Constitutional Accountability Center, seeks to declare Whitaker’s appointment unconstitutional and block him from serving as acting AG — a position which puts him in charge of Special Counsel Robert Mueller’s investigation into Russian meddling in the 2016 election. 

Arguing that Whitaker’s appointment “so flagrantly defies constitutional law that any viewer of School House Rock would recognize it,” Blumenthal accused Trump of denying senators their constitutional obligation of scrutinizing the nomination.

“Americans prize a system of checks and balances, which President Trump’s dictatorial appointment betrays. … The reason is simple: Whitaker would never pass the advice and consent test,” he said in a statement. “In selecting a so-called ‘constitutional nobody’ and thwarting every senator’s constitutional duty, Trump leaves us no choice but to seek recourse through the courts.”

Whitehouse, meanwhile, contended that “the stakes are too high to allow the president to install an unconfirmed lackey to lead the Department of Justice — a lackey whose stated purpose, apparently, is undermining a major investigation into the president.”

Hirono said she and her colleagues want to court to clarify that the U.S. Senate must confirm Whitaker’s appointment as acting AG for the White House to prevent violating the Constitution’s Appointments Clause.

Trump announced earlier this month that Whitaker would take over for Jeff Sessions as the new acting attorney general before a permanent replacement is “nominated at a later date.”

Sessions, whom Trump repeatedly criticized for recusing himself from the Russia probe, resigned at the president’s request.

The appointment drew criticism from some, including U.S. Sen. Ed Markey, D-Massachusetts.

The state of Maryland, meanwhile, has also reportedly challenged Whitaker’s appointment in court, arguing that Trump went around the Constitution and Justice Department’s succession plan in naming him acting AG.