U.S. President Barack Obama (left) and Attorney General Eric Holder attend the 32nd annual National Peace Officers' Memorial Service at the West Front Lawn at the U.S. Capitol, May 15, 2013 in Washington, DC. Obama delivered remarks at the event, invoking the law enforcement officers who worked to bring the Boston Marathon bombing suspects to justice. Olivier Douliery - Pool/Getty Images

U.S. Attorney General Eric Holder, the first African-American to serve in the position, is expected to announce his resignation Thursday. Holder, one of the longest-serving cabinet members under President Barack Obama, will likely remain in office until a successor is nominated and confirmed, according to media reports. The question now is who will replace Holder as the nation's top law enforcement official?

Some possible candidates include: U.S. Secretary of Education Arne Duncan; California Attorney General Kamala Harris; retiring U.S. Attorney Jenny Durkan in Seattle; Kathryn Ruemmler, the former White House counsel; Gov. Deval Patrick of Massachusetts; and Donald B. Verrilli Jr., the current U.S. solicitor general. Other likely appointees are former Gov. Jennifer M. Granholm of Michigan; Sen. Sheldon Whitehouse, a former Rhode Island attorney general; Deputy U.S. Attorney General James Cole; Manhattan U.S. Attorney Preet Bharara; and Loretta E. Lynch, the U.S. attorney in Brooklyn.

Washington will likely debate the names until Obama unveils his top pick. Patrick, who is preparing to retire after eight years as governor of Massachusetts, would be a natural choice, according to NBC News. He and Obama have been close friends for years and both have helped each other in their respective recent campaigns. Ruemmler, however, was spotted having dinner with Holder last month, a potential clue, the Wall Street Journal reports. Verrilli, meanwhile, defended Obama's Affordable Care Act before the Supreme Court in 2012 and emerged victorious. That could be worth an attorney general appointment.

It's unclear how much more time Holder has at the Justice Department. Obama could move to appoint a successor before the midterm elections in November, when Republicans hope to win back the Senate majority. After a rule change last year, the Senate can now confirm the president's executive-branch nominees with a simple majority -- not the 60 votes it generally needs to get legislation passed.

A senior White House official told the New York Times Thursday that the president was “a long way” from announcing Holder’s successor.