CNN  — 

US District Court Judge Emmet Sullivan, who is overseeing former national security adviser Michael Flynn’s criminal lying case, has retained a Washington, DC, law firm run by well-known trial lawyer Beth Wilkinson to help him respond to the appeals court about the Flynn case, according to a person familiar with the arrangement.

It’ll be a high profile legal assist in what’s become one of the most unusual and polarizing criminal matters in DC federal court in years.

The Justice Department earlier this month agreed with Flynn that it should drop his prosecution for lying to the FBI about his 2016 transition-era calls with the then-Russian ambassador. But Sullivan has hesitated, instead appointing an outside lawyer to argue against the Justice Department’s dismissal request and weigh whether Flynn may have committed perjury in his statements to the court.

Flynn and DOJ-backers have asserted that the case can’t continue if prosecutors want to abandon it. But others, including Sullivan’s outside appointee, have said the judge could sentence Flynn since he already pleaded guilty, and have questioned the DOJ’s move as a largely political one. Sullivan has set a schedule to keep the case in court at least into July.

Flynn challenged Sullivan’s plans last week, going directly to the appeals court about the trial-level judge. That’s when an appellate panel gave the surprising order for the judge to explain to them by June 1 his stance and his power over the case.

The small firm, Wilkinson Walsh, will be writing a legal argument on Sullivan’s behalf after the appeals court last week gave him the unusual order to defend his authority, the person said.

The three-judge appellate panel includes two Republican-appointed judges who’ve been sympathetic to the Trump administration regarding cases related to the Mueller investigation — and they may be inclined to push back against Sullivan as Republican criticism of the judge has grown.

The Washington Post on Saturday first reported Wilkinson’s role in the Flynn case.

Wilkinson is one of the most prominent litigators in Washington. She rose to prominence prosecuting Oklahoma City bomber Timothy McVeigh under the supervision of later-Circuit Judge Merrick Garland.

More recently, Wilkinson’s firm represented now-Supreme Court Justice Brett Kavanaugh for his confirmation hearings.

Wilkinson is married to CNN contributor David Gregory.