The submission of a 28-page questionnaire to the Senate Judiciary Committee by the interim United States attorney for the Eastern District of Virginia, Lindsey Halligan, suggests that President Trump is determined to retain the prosecutor — even if it means precipitating a clash with his own party over the Senate custom known as “blue slips.”

A “blue slip” is a form used by the Senate Judiciary Committee to solicit the views of senators on a presidential nominee for a federal judgeship or a United States Attorney position. The history of the blue slip is Byzantine, but in its current incarnation it allows a single senator to block the nomination of a judge or chief federal prosecutor in their state, even if they are from a rival political party to the president’s. Ms. Halligan’s appointment is being blocked by Virginia’s two Democratic senators, Mark Warner and Tim Kaine,

Judge Cameron McGowan Currie, a South Carolina-based appointee of President Clinton, last month ruled that Ms. Halligan was unlawfully appointed — and dismissed the criminal charges she secured against the former director of the FBI, James Comey, and New York’s attorney general, Letitia James. The Department of Justice has appealed that ruling, which was a setback for Attorney General Pam Bondi’s efforts to convict the two antagonists of Mr. Trump.

Ms. Halligans’s Achilles heel — at least according to Judge Currie — was that she is the second consecutive interim appointment selected to lead the Eastern District of Virginia. Federal law appears to mandate that the Executive Branch can make one, but not two, such appointments, to last for 120 days. Once that deadline expires, the task of appointing a prosecutor falls to the federal judges in the district. Permanent can only be secured by Senate confirmation.

To get to that vote, though, the blue slip tradition requires that both of a state’s senators, no matter their party, assent to put forward the nomination. Ms. Halligan’s path to a vote in the Senate, of course,  is blocked by Messrs. Kaine and Warner. Given the political sensitivities of the prosecutions of Ms. James and Mr. Comey, and Ms. Halligan’s prior role forcing changes to exhibit language at the Smithsonian’s National Museum of African American History and Culture, a stone’s throw from liberal Northern Virginia, it’s unlikely the two men will be swayed. 

Messrs. Kaine and Warner both supported Ms. Halligan’s predecessor, Erik Siebert, who was also serving on an interim basis. He resigned, though, reportedly over his reluctance to bring the cases against Mr. Comey and Ms. James. Mr. Trump declared on social media that “He didn’t quit, I fired him!” The president mentioned the prosecutor’s support from Virginia’s Democrats as the reason for his termination. 

Mr. Trump last month said at the White House that  “They should get rid of blue slips. If you have one Democrat in a state, it is not possible to appoint because of blue slips.” He added that the custom “should not be relevant anymore. This is a different world than it was 15, 20 years ago. That was a gentleman and gentlewoman’s world. This is a little bit different, unfortunately.”

That position was buttressed by Vice President J.D. Vance, who called blue slips “The single biggest obstacle to prosecuting violent leftists is judges and prosecutors in deep blue areas who think violence is OK if you’re a leftist. This is why we must get rid of the blue slip process.” Senator Charles Grassley, in defending the blue slip, insists that what Mr. Trump “needs to do is continue what’s worked for the last 50 years.” 

The refusal of Democrats to grant blue slips has left large swaths of Mr. Trump’s DOJ in legal limbo. Most of the country’s 93 United States attorney’s offices are being led by interim leaders. The interim prosecutor in New Jersey, Alina Habba, was also disqualified by both a trial judge, Matthew Brann, as well as the Third United States Appeals Circuit. Ms. James is also mounting a challenge to the appointment of the interim United States attorney in upstate New York, John Sarcone. 

Ms. Habba’s chances of securing a blue slip from the Garden State’s two  Democratic senators was likely precluded by the criminal charges she brought against two other high-profile, black Democrats, the Mayor of Newark, Ras Baraka, and Congresswoman LaMonica McIver. The charges followed a brawl at an ICE facility. The case against Mr. Baraka was dropped, but the one against Ms. McIver – a felony case which could lead to prison time –  is ongoing and has survived her motions to dismiss.

Ms. Habba resigned from her post following her disqualification, though she warned  “do not mistake compliance for surrender” and that “While I was focused on delivering real results, judges in my state took advantage of a flawed blue slip tradition and became weapons for the politicized left.” Ms. Habba is now advising Ms. Bondi at Main Justice, where she’d previously been investigating the Biden White House’s use of the autopen prior to her appointment to the role in New Jersey. 

Ms. Halligan’s submitting of her questionnaire to the Senate was accompanied by a statement from White House Press Secretary that “She’s the President’s nominee. It is our hope that she is confirmed and submitting her questionnaire is part of that process.” Mr. Trump ventured that “Blue Slips are making it impossible to get great Republican Judges and U.S. Attorneys approved to serve in any state where there is a single Democrat Senator!”

The Senate majority leader, John Thune, has poured cold water on abolishing the custom. He reckons that “There are many Republican senators, way more Republican senators who are interested in preserving” blue slips than those eager to relegate it to history’s dust bin.