Washington (CNN)Sen. Barbara Mikulski, the longest serving female senator in history, will retire at the end of her term.
Barbara Mikulski, the longest serving female senator in history, to retire
The Maryland Democrat made the announcement Monday morning in her hometown of Baltimore.
Mikulski, 78, is known as the "Dean" of the Senate women -- helping forge bipartisan relationships for decades that often result in compromise. Until Democrats lost control of the Senate, she was the chairman of the powerful Senate Appropriations Committee.
"I had to ask myself this question: Am I campaigning for me, or am I campaigning for my constituents?" she said Monday. "Am I raising money or raising hell?"
President Barack Obama praised Mikulski as "legendary" and called her "an institution in the United States Senate" in a statement Monday that followed her announcement.
"Barbara's service to the people of Maryland spans decades, but her legacy will span generations," Obama said. "Barbara is the longest serving woman in Congress, and her leadership serves as an inspiration to millions of women and girls across the globe to stand up and lead."
Her retirement could present an opening for former Maryland Gov. Martin O'Malley, who left office weeks ago and has been considering a 2016 bid for the Democratic presidential nomination -- though he could struggle to make waves in that race if, as expected, Hillary Clinton runs.
It's not clear whether O'Malley would be interested in a legislative seat. But his mother has long served as Mikulski's receptionist in her Washington office. And O'Malley tweeted his praise for Mikulski on Monday.
The state is also represented by seven Democratic House members -- including Rep. Chris Van Hollen, a member of the party's congressional leadership -- and they could all scramble for the seat, too.
O'Malley's former lieutenant governor, Anthony Brown, is another contender. Also on the list of potential Democratic candidates are Baltimore Mayor Stephanie Rawlings-Blake and Labor Secretary Tom Perez.