WASHINGTON (Reuters) - The state of Maryland launched a court challenge on Tuesday to the legality of President Donald Trump’s appointment of Matthew Whitaker as acting U.S. attorney general, saying the president overstepped his constitutional authority and broke federal law.

FILE PHOTO: Acting U.S. Attorney General Matthew Whitaker is pictured in an undated photo obtained by Reuters, Nov. 8, 2018. Courtesy U.S. Department of Justice/via REUTERS/File Photo/File Photo

Trump installed Whitaker as acting attorney general last week after ordering Jeff Sessions to resign from the post. Trump had repeatedly criticized Sessions for recusing himself in March 2017 from the federal investigation, now headed by Special Counsel Robert Mueller, into Russia’s role in the 2016 U.S. election, a probe Trump has called a “witch hunt.”

Congressional Democrats have voiced concern that Whitaker, a Trump loyalist, could undermine or even fire Mueller.

Maryland asked U.S. District Judge Ellen Hollander in Baltimore to bar Whitaker from appearing in an official capacity as acting attorney general in its ongoing lawsuit against the administration over the Affordable Care Act healthcare law. The state asked the judge to substitute Deputy Attorney General Rod Rosenstein in Whitaker’s place.

The city of San Francisco, also involved in litigation against the Trump administration, on Monday told the Justice Department it may sue to challenge Whitaker’s appointment.

Whitaker’s elevation as the top U.S. law enforcement official gives him, rather than Rosenstein, authority over Mueller’s investigation, which already has led to criminal charges against a series of former Trump aides and has cast a cloud over Trump’s presidency.

Whitaker, who had served as chief of staff for Sessions, previously questioned the scope of Mueller’s investigation and spoke about the idea of reducing funding for the special counsel so the probe “grinds to almost a halt.”

Maryland Attorney General Brian Frosh, a Democrat, said the state plans to challenge Whitaker’s appointment on two legal grounds.

Maryland argues that Rosenstein, the department’s No. 2 official, should have succeeded Sessions under a federal succession law that vests full authority in the deputy attorney general should the office of attorney general become vacant. The state also argues that the Republican president violated the so-called Appointments Clause of the U.S. Constitution because the job of attorney general is a “principal officer” who must be appointed by the president and confirmed by the Senate.

Maryland’s legal filing states that Trump “might reasonably be seen as appointing a loyalist in a way that deliberately circumvents the Senate’s constitutional advice-and-consent role.”

White House communications director Mercedes Schlapp told Fox News on Tuesday Trump had “full and legal authority” to appoint Whitaker.

‘UNQUALIFIED AND UNCONFIRMED’

“The Attorney General’s succession statute and the Constitution protect the country against exactly what President Trump has attempted to do here - pluck an unqualified and unconfirmed partisan to be the nation’s chief law enforcement officer in order to protect himself rather than the rule of law,” Frosh said in a statement.

Maryland’s challenge came as part of its litigation filed against the administration in September after Sessions declined to defend the Affordable Care Act’s protection of people with pre-existing medical conditions in a separate lawsuit led by Texas. The Affordable Care Act is often called Obamacare.

Frosh and the Democratic attorney general for the District of Columbia are pursuing separate litigation alleging that Trump’s business dealings have violated a constitutional anti-corruption provision.

Senator Dianne Feinstein, the top Democrat on the Senate Judiciary Committee, on Tuesday called on the panel’s Republican chairman, Senator Chuck Grassley, to quickly hold hearings with Whitaker and Sessions, who was ousted by Trump a day after his party lost control of the House of Representatives in midterm congressional elections.

The circumstances surrounding the departure of Sessions “raise serious questions” about the legality of Whitaker’s appointment and possible impact on Mueller’s investigation, Feinstein wrote in a letter to Grassley.

Grassley last week said he looked forward to working with Whitaker, a former federal prosecutor in the senator’s home state of Iowa who he has known for years.

Democrats and other critics urged Whitaker to step aside from overseeing Mueller’s investigation. On Monday, the Justice Department said Whitaker would consult with ethics officials about any matters that could require recusal.

A Justice Department spokeswoman declined to comment on the litigation. The department is expected in the near future to issue a legal opinion defending Whitaker’s appointment.

With Sessions recused, Rosenstein appointed Mueller after Trump fired James Comey as FBI director in May 2017. The FBI had been in charge of the Russia probe.