Who are the candidates to succeed Barbara Mikulski?

Ben Carson, a retired neurosurgeon from Johns Hopkins Hospital, could eye a Senate seat. The Republican moved to Florida but still has a house in Baltimore County. But the likelihood of his running may have taken a hit when the day after Mikulski's announcement, Carson said that he is formally exploring a run for president.

Former Gov. Robert L. Ehrlich Jr. has been out of politics but still on the political circuit, giving his speeches and visiting early primary states such as New Hampshire. The Republican also has written a book: America: Hope for Change.

Rep. Andy Harris, the only Republican on Maryland's delegation, would be taking a gamble by running in the heavily Democratic state, as he would lose his House seat if he loses.

Rep. Chris Van Hollen established a national profile as chairman of the Democratic Congressional Campaign Committee. Since then he has taken other leadership posts, including the ranking member on the Budget Committee.

Rep. John Sarbanes has name recognition in the state because of his father, Paul, the former U.S. Senator.  Reps. Elijah Cummings and C.A. Dutch Ruppersberger are other Democrats who could make a run for the upper chamber.

Rep. John Delaney, a Democrat and businessman, would have a personal war chest that he could tap in the event of another run for office, as he did in the last election. He co-founded CapitalSource, a commercial lender.

Dan Bongino, the former Secret Service agent who lost to Delaney in a House race last year, also could be up for another run.

Rushern L. Baker III has built a profile in the Democratic party and could seek higher office after two terms as Prince George's County Executive.

Former First Lady Kendel Ehrlich has flirted with the idea of running for public office in recent years, and retains considerable name recognition.

Kweisi Mfume, the former city councilman, Congressman and head of the NAACP, may be interested in a higher-profile role after being named as the chairman of the board or regents at Morgan State University in 2013.

Other names that may surface after recent defeats while campaigning for higher office: Former gubernatorial candidates like former Lt. Gov. Anthony Brown, former Attorney General Doug Gansler and former Del. Heather Mizeur, as well as Brown's running mate, former Howard County Executive Ken Ulman.

Who isn't on the list? Former Gov. Martin O'Malley says he won't run for Mikulski's seat. He is openly considering a run for president, but the Democrat had long been thought to be eying Mikulski's seat, which could have been a launching pad for a 2020 bid for the White House.