WASHINGTON (Reuters) - Matthew Whitaker flew to Dallas last week to deliver his latest speech since U.S. President Donald Trump installed him as acting attorney general, an appointment embroiled in criticism and court challenges.

FILE PHOTO: Acting Attorney General Matthew Whitaker speaks to state and local law enforcement on efforts to combat violent crime and the opioid crisis in Des Moines, Iowa, U.S., November 14, 2018. REUTERS/Scott Morgan/File Photo

In the aftermath of the blow-up, Whitaker’s public remarks in the last five weeks have been notable for what they lacked - any hint of controversy.

Whitaker’s speeches, which have to largely stuck to conventional subjects such as opioid crisis, reflect the inconspicuous approach adopted by the 49-year-old lawyer since Trump named him as the nation’s top law enforcement official.

So far, fears among some Democrats that Whitaker would interfere with an investigation into whether Trump’s presidential campaign colluded with Russia have not come to pass. He’s waded into few legal issues, and largely stayed the course set by his predecessor, ousted Attorney General Jeff Sessions.

Meanwhile, the initial criticism of his appointment, centered partly on his lack of credentials and questions about his conflicts of interest in the Russia probe, has turned into a constitutional fight.

There are at least nine cases questioning the legality of his appointment, many of which contend Trump violated the U.S. Constitution by installing him without Senate confirmation. Two of those are slated for oral arguments this week in federal courts, while a third case was argued on Friday morning

Those court fights appear to have limited Whitaker’s reach, experts say, since almost any action he takes could be challenged and put on hold.

“It’s quite possible, although we’ll never really know, that the controversies surrounding his appointment have had a chilling effect on Whitaker,” said George Conway, an attorney who is married to White House adviser Kellyanne Conway.

Conway is among those who believe the appointment violated the Constitution.

“One of the reasons he is not making any sudden moves is because of the question mark over him,” said Victoria Bassetti, a contributor with the Brennan Center for Justice, a judicial advocacy group at New York University.

“As long as these cases are pending, they are acting as sort of a guard rail,” she said.

Whitaker declined an interview request.

A Justice Department spokeswoman, Kerri Kupec, said in a statement that Whitaker has “worked tirelessly to maintain the momentum and achieve the priorities” of the department and cited examples including his meetings with U.S. Attorneys offices and the creation of a Memphis Crime Gun Strike Force, among other things.

ATTENTION ON IMMIGRATION

One of the few areas where Whitaker has sought to make policy during his brief tenure is immigration, where he singled out two cases in early December for special attention.

Since U.S. immigration courts fall under the Justice Department’s jurisdiction, the attorney general can intervene and help set precedents.

But the controversy surrounding Whitaker’s appointment could complicate the two cases he has selected to review.

One of them, called Matter of Castillo-Perez, turns on whether multiple drunk-driving convictions should disqualify an immigrant seeking relief from deportation proceedings. The other, known as the Matter of LEA, is focused on whether immigrants may seek asylum because their membership in a family is central to why they face persecution.

Bradley Jenkins, a lawyer with the Catholic Legal Immigration Network representing LEA, said he anticipates challenging Whitaker’s authority to review the case.

“We are certainly concerned at the aggressiveness with which this person, who was appointed via an unprecedented procedure, seems eager to exercise one of the powers of the office in an acting capacity,” Jenkins said.

It remains to be seen whether Whitaker will issue a decision on his reviews before he leaves the post. Earlier this month, Trump said he will nominate William Barr, who was attorney general under former President George H.W. Bush, to fill the job.

Some critics say that nomination should not negate concerns about Whitaker and any actions he may take, including on these two cases.

“The attorney general has an enormous amount of power vested in him,” said Ben Berwick, a lawyer with Protect Democracy, one of the groups leading a legal challenge to Whitaker’s appointment filed by three Senate Democrats.

Berwick added that Whitaker probably has a few more months in the job before Barr’s nomination is considered by the Senate.

“Someone who wields that much power in this country needs to be approved by the Senate,” he said.

The legal challenges to Whitaker mostly center on whether Trump violated the “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.

They also allege he violated a succession statute which calls for the deputy attorney general - in this case Rod Rosenstein - to take over temporarily as acting attorney general.

The Justice Department has defended Whitaker’s appointment, saying Trump is allowed to install a senior, non-Senate confirmed staffer temporarily under the Federal Vacancies Reform Act.

So far, one judge has sided with the Justice Department by declaring Whitaker’s appointment was constitutional, after a defendant in a criminal case tried to have the charges dismissed.

There are still a number of pending cases, however, including two this week, and the lawsuit brought by the three Senators who say they were denied their right to provide advice and consent.

Legal experts said it is possible many of these lawsuits could be rendered moot if the Senate acts quickly to confirm Barr.

But some say it is important that a judge make a ruling, or else future presidents could seek to sidestep Senate confirmation.

“If a president can fire a cabinet member and replace them with staffers who have never been reviewed by the Senate, that is a major historical precedent,” said Walter Dellinger, a former solicitor general.