Vincent H. Cohen Jr., principal assistant U.S. attorney, left, and Ronald C. Machen Jr., U.S. attorney for the District of Columbia in 2012. Cohen is now acting U.S. attorney and faces tough competition for the permanent job. (Ricky Carioti/The Washington Post)

The District’s acting top prosecutor is facing tough competition as he seeks to continue to lead the largest U.S. attorney’s office in the nation, according to people familiar with the selection process.

Acting U.S. Attorney Vincent H. Cohen Jr. is among three lawyers who interviewed for the position. Others seeking the job are Channing D. Phillips, a ­former acting U.S. attorney in the District, and Christopher ­Zampogna, a former New York prosecutor who runs a D.C-based civil litigation firm.

A federal committee that interviewed the men in May recommended Cohen and Phillips as their top choices, according to three people involved in the committee process. Del. Eleanor Holmes Norton (D-D.C.) sent her picks to the White House, which has yet to announce its selection.

President Obama’s pick will succeed Ronald C. Machen Jr., who resigned as U.S. attorney in April after five years and returned to private practice.

Cohen, 45, a onetime defense attorney who was Machen’s deputy, has overseen the prosecutions of violent crime and public corruption cases — including those against three former D.C. Council members who ultimately were convicted.

Channing Phillips, then-principal assistant with the U.S. attorney's office, second from left, joins inspector Matthew Klein, director of Internal Affairs, left, Police Chief Cathy L. Lanier and Mayor Adrian Fenty to discuss an investigation in 2007. (Nikki Kahn/The Washington Post)

Phillips, 57, a senior adviser to U.S. Attorney General Loretta E. Lynch, worked as a D.C. prosecutor beginning in the mid-1990s, handling drug, fraud and violent crime cases. For years he was the public face of the office, acting as spokesman during high-profile cases, including the slaying of D.C. intern Chandra Levy.

Looming over the selection process are potential implications for the four-year investigation of former D.C. mayor Vincent C. Gray. During Machen’s term, prosecutors publicly accused Gray of having detailed knowledge of a “shadow campaign” to illegally funnel more than $660,000 into his 2010 get-out-the-vote campaign. Gray has called the allegations “lies.”

During the course of the investigation, which Cohen has been involved in, several of Gray’s aides have been prosecuted. But there have been no charges filed against the former mayor or an announcement that the investigation has ended. Gray and his supporters have suggested that the case played a role in Gray’s loss in the 2014 Democratic primary.

Council member Mary M. Cheh (D-Ward 3), who previously has criticized prosecutors for allowing the Gray investigation to drag on, said that she believes the handling of the case could derail Cohen’s chances of being named U.S. attorney.

“Mr. Cohen has good experience. But this issue about the investigation is of singular importance in determining fitness for the top spot.

“Unless whoever is making the recommendation is satisfied that Mr. Cohen had no role in this or some explanation to make this delay palatable, then it should be disqualifying,” Cheh said.

But others defended Cohen’s work. As deputy, Cohen helped oversee the prosecutions of three former D.C. Council members — Harry Thomas Jr., Kwame Brown and Michael A. Brown — on federal corruption charges. As a deputy and as an acting U.S. attorney, he has overseen murder and drug cases.

“He should be judged on the totality of his work as a prosecutor,” said D.C. Attorney General Karl A. Racine, a Cohen supporter. Since taking over the job in April, Racine said, Cohen has committed federal resources, including help from the U.S. Drug Enforcement Administration, to help the District fight synthetic drugs.

“While Vincent Gray is important, what is most important is the totality of his commitment to D.C. and his job as a community prosecutor,” he said. “And on those measures, I find him to be an exceptional lawyer and public servant.”

Jeffrey A. Taylor, a former U.S. attorney for the District, said the decision to move forward with the Gray investigation or to end it depends on the assessment of the evidence.

“If there is evidence to move forward, move forward. If not, then it’s time to move on. It shouldn’t matter who the U.S. attorney is,” said Taylor, who served as the city’s top prosecutor from 2006 through 2009. “The timing shouldn’t depend on who is in the chair.

“The decision should be driven by the facts and the evidence and the applicable law,” Taylor said.

In addition to taking over the Gray investigation, the next U.S. attorney also will head a busy office handling several other high-profile matters. The District office is the only one in the nation that handles federal and local cases.

Prosecutors there are focusing on the case of Ahmed Abu Khatallah, who is accused in the 2012 attack on U.S. facilities in Benghazi, Libya, which killed four Americans. They also are preparing for a retrial of Ingmar Guandique, who is accused in Levy’s 2001 killing. Earlier this year, a judge granted Guandique a new trial after it was revealed that a key witness in the first trial had lied.

The office also is handling prosecutions related to a recent spike in violent crime in the District. Among those is the case of a man charged in the May slayings of Northwest Washington businessman Savvas Savopoulos, his wife, his 10-year-old son and the family’s housekeeper.

At a Congressional Black Caucus reception last week, Norton declined to comment on the selection process. “It’s up to the White House now,” she said.

Zampogna said Norton’s office asked him to submit his name for the position.

“I was honored her office asked me to do this,” he said.

Zampogna, 48, called the interview process with the selection committee “one of the hardest things I have ever been through.”

He said one of the biggest issues the committee asked him about was keeping morale high among prosecutors.

“I can tell you if you’re in an office with bad morale, you start losing assistants. That creates more problems,” he said. “The whole office then isn’t going to be training people to get to the next level with seasoned prosecutors.”

Both Cohen and Phillips declined to comment.

Former U.S. attorney general Eric H. Holder Jr. first hired Cohen as a prosecutor in 1997, when Holder served as U.S. attorney for the District. After six years with the office, Cohen joined the defense side at Hogan & Hartson. In 2010, Machen brought Cohen back to the office as his deputy, with plans at the time of grooming Cohen for the top job.

Phillips joined the U.S. attorney’s office in 1994, working his way up from his job as a prosecutor. In 2009, he also briefly served as acting U.S. attorney, including overseeing the prosecution of Washington Wizards star Gilbert Arenas, who pleaded guilty to felony gun possession following a 2009 altercation with a teammate.

In 2010, after Phillips was passed over for the top spot, he went to work for the Justice Department as Holder’s senior adviser.

An announcement from the White House could be made in the coming weeks.