WASHINGTON (AP) — Maryland's former governor announced Tuesday he will not seek the seat of a retiring senator, keeping open his option of running for president in a Democratic primary likely to include Hillary Rodham Clinton.

Sen. Barbara Mikulski of Maryland announced plans to retire on Monday, giving Martin O'Malley an alternate path if he wanted to avoid what looks today to be a longshot bid against Clinton.

O'Malley said in a statement he was "hopeful and confident that very capable public servants with a desire to serve in the Senate will step up as candidates for this important office. I will not be one of them."

Mikulski's surprise decision came as O'Malley has been gearing up toward a presidential campaign with upcoming appearances in New Hampshire and Iowa — early voting states in the primary process.

Little known outside his home state, O'Malley has yet to gain much traction in a hypothetical matchup against Clinton, who has a network of super PACs — organizations that are allowed to spend unlimited funds to support candidates or legislation independently — already working on her behalf. Much of the party's establishment is eagerly waiting for the former secretary of state to announce her candidacy. Those pining for someone other than Clinton have largely focused their longing not on O'Malley, but Massachusetts Sen. Elizabeth Warren — who tells everyone who asks she isn't running.

O'Malley has deep ties to Mikulski, the longest serving woman in the history of the U.S. Congress. While in law school, he served as field director on her first Senate campaign in 1986, and his mother Barbara has worked as a receptionist in Mikulski's Washington office since 1987. Yet the retiring senator has already endorsed Clinton for 2016.

Before the announcement, O'Malley allies noted that the former governor had always enjoyed the role of executive, having served as Baltimore's mayor for seven years before becoming governor in 2007. He has shown little interest in the past in serving in Congress.

O'Malley has said he will make a final decision on a presidential campaign this spring.