Three Democratic senators on Monday filed a lawsuit in federal court challenging the constitutionality of President Trump’s appointment of Matthew Whitaker as acting attorney general.

Whitaker was appointed by Trump to lead the Justice Department after Attorney General Jeff Sessions was forced out of the role earlier this month.

Connecticut Sen. Richard Blumenthal, Rhode Island Sen. Sheldon Whitehouse and Hawaii Sen. Mazie Hirono filed the complaint against Whitaker in the U.S. District Court for the District of Columbia on Monday. All three issues fiery statements.

“Installing Matthew Whitaker so flagrantly defies constitutional law that any viewer of School House Rock would recognize it. Americans prize a system of checks and balances, which President Trump’s dictatorial appointment betrays,” Blumenthal said.

"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,” Whitehouse said.

“Donald Trump cannot subvert the Constitution to protect himself and evade accountability,” Hirono said.

The senators argue that Whitaker’s appointment is in violation of the Constitution’s appointments clause. They ask the federal court to declare Whitaker’s appointment unconstitutional and block him from carrying out duties.

But the Justice Department maintains that the appointment is legal. DOJ spokeswoman Kerri Kupec said Monday the appointment is “lawful” and comports with the Federal Vacancies Reform Act, the appointments clause of the U.S. Constitution, Supreme Court precedent, past Department of Justice opinions and past actions of Republican and Democratic presidents.

“There are over 160 instances in American history in which non-Senate confirmed persons performed, on a temporary basis, the duties of a Senate-confirmed position,” Kupec said. “To suggest otherwise is to ignore centuries of practice and precedent.”

Last week, the Justice Department Office of Legal Counsel issued an opinion supporting Whitaker’s appointment.

DOJ SAYS MATTHEW WHITAKER CAN SERVE AS ACTING ATTORNEY GENERAL

“This office previously had advised that the president could designate a senior Department of Justice official, such as Mr. Whitaker, as Acting Attorney General,” the OLC said, noting that Whitaker has been serving at the Justice Department “at a sufficiently senior pay level for over a year.”

Others have filed lawsuits over the Whitaker appointment, including the state of Maryland.

For more than a year, Trump repeatedly lambasted Sessions over his recusal from the Russia investigation, saying he wouldn’t have installed him as the country’s top law enforcement officer had he known his attorney general would recuse himself from the Russia probe.

Democrats have expressed alarm about what the change at DOJ could mean for the Russia probe, with Senate Minority Leader Chuck Schumer, D-N.Y., saying, “protecting Mueller and his investigation is paramount.”

Other Democrats have called on Whitaker to remove himself from the Russia probe because of his past comments expressing skepticism about the scope and appropriateness of the probe.

The Democratic senators are being represented by two non-profit law firms in the case: Protect Democracy and the Constitutional Accountability Center.

Fox News’ Jake Gibson, Brooke Singman, Paige Dukeman and Bill Mears contributed to this report.