President Donald Trump speaks as acting attorney general Dana Boente, right, listens during a meeting Feb. 7 with county sheriffs in the Roosevelt Room of the White House. (Jabin Botsford/The Washington Post)

A Democratic senator from Delaware has asked the Justice Department to explain why Dana Boente was asked last month to resign as U.S. attorney for the Eastern District of Virginia.

Boente, who has also been serving as acting chief of the Justice Department's National Security Division, announced last month that he will step down when a replacement is confirmed. He had been asked to do so by the Trump administration, several people with knowledge of the conversations confirmed.

"I cannot take on faith that this dismissal was normal or justified," Sen. Christopher A. Coons (D-Del.) wrote in a Nov. 7 letter to top Justice Department officials. "The Department of Justice and the White House should provide their reasoning for why someone like this, who was initially asked to continue serving in his important role, was suddenly forced to resign."

Coons noted that U.S. attorneys serve at the pleasure of the president but questioned the timing of the move. News of Boente's resignation came just hours before CNN reported that special counsel Robert S. Mueller III's office had brought the first ­charges in the Russia investigation — fueling immediate speculation that the two were somehow connected.

While aspects of the investigation initially involved the U.S. attorney's office in Alexandria, it is now being handled by the special counsel's office and the cases made public are in federal court in the District.

Coons asked for a response by Nov. 21.

While it is typical for a new president to ask for resignations of U.S. attorneys to make way for new appointees, Boente had previously been told by Attorney General Jeff Sessions that he could remain in his Virginia post as long as he liked, according to two people familiar with those conversations.

But several weeks ago, the administration reversed that stance, instead offering him other jobs. One of the jobs suggested was a leadership post at the U.S. Marshals Service, according to two people familiar with the offer.

A part of Mueller's probe had indeed emanated from the office that Boente supervises, though at the time his departure was announced, the investigation had been fully taken over by Mueller.Boente, too, has been a loyal soldier of the administration — defending the president's controversial travel ban when another Obama administration holdover wouldn't and even carrying out the order to fire other U.S. attorneys.

People who had spoken with Boente and were familiar with the process to replace him said, as far as they understood, his removal was unconnected to anything related to Mueller.

Boente is the only U.S. attorney left in the country who was nominated by President Barack Obama.

Another reason Boente's announcement attracted attention was the controversy over the administration's removal of Preet Bharara, former U.S. attorney for the Southern District of New York. Bharara was given similar assurances that he could stay before being asked in March to step down. He refused and was fired.

Boente had early on assumed that he would not last in his position regardless of who won the election. But in January, acting attorney general Sally Yates was fired for refusing to defend President Trump's ban on travel from six majority-Muslim countries. Boente accepted an offer to step in as the acting attorney general at a critical time for the administration.

"Dana, I want to thank you for your service," Trump said at a White House roundtable in February. "Amazing the way you just stepped into the breach and have done such a good job."

Once Sessions was confirmed as attorney general, Boente moved to the deputy slot. It was from that position that he asked 46 other U.S. attorneys around the country to resign. In fact, it was Boente who called Bharara and fired him.

When Rod J. Rosenstein was confirmed as deputy attorney general, Boente became acting head of the National Security Division. He will step down from that post when Boeing counsel John Demers is confirmed.

While Boente worked in the Trump administration, Rep. Bob Goodlatte (R-Va.) had already assembled a "panel of distinguished Virginians" to interview candidates for his replacement as U.S. attorney. In March, on behalf of Virginia's Republican congressional delegation, he sent a letter to Trump recommending four: Brian Benczkowski, Chuck James, Laura Marshall and Zach Terwilliger. (Benczkowski has since been nominated to lead the Justice Department's Criminal Division.)

The remaining three have all worked as assistant U.S. attorneys. James was a prosecutor in Richmond and in the Justice Department's Criminal Division; he was also deputy to former Virginia attorney general Ken Cuccinelli II. He is now a partner at the firm Williams Mullen.

Marshall spent 15 years in white-collar prosecution and is now at the firm Hunton & Williams. Terwilliger worked in major crimes and is now associate attorney general of the Justice Department's Criminal Division.

It is Virginia's two Democratic senators, however, who are charged with recommending candidates for the position; their application process ends Nov. 17.