BALTIMORE (AP) — Sen. Barbara Mikulski, a tough and dogged daughter of working class Baltimore who rose to become the longest-serving woman in the history of Congress, said she had one question as she weighed seeking a sixth term: "Do I spend my time raising money, or do I spend my time raising hell?"

The 78-year-old Maryland Democrat, who led the powerful Appropriations Committee, announced Monday that she'd decided on the latter approach and would not seek re-election next year when her fifth term ends.

"I don't want to spend my time campaigning for me," she said at a news conference in Fells Point, the now-trendy waterfront neighborhood where her parents had a grocery store and her immigrant grandparents ran a bakery. It's also where Mikulski got her first taste of politics leading an effort to stop an expressway from coming through. "I want to campaign for the people."

Her announcement opens the way for what could be a raucous fight next year to replace her in Maryland's first open Senate seat in a decade. Potential candidates include former governors — Democrat Martin O'Malley and Republican Bob Ehrlich — and current House members, among them Democrats Chris Van Hollen and Donna Edwards and Republican Andy Harris.

Although Maryland voters lean heavily Democratic, especially in presidential election years, the state elected a Republican governor last fall and Republicans insist they will compete hard in the Senate race.

The pugnacious Mikulski, who stands less than five feet tall, has for years been a force to be reckoned with on Capitol Hill, barreling through the halls while gruffly ordering people aside en route to committee hearings and news conferences.

She is not one for social niceties and her prickly personality does not always endear, yet she won the devotion of Maryland voters as she advocated forcefully for her constituents, from Chesapeake Bay watermen to NASA scientists at the Goddard Space Flight Center. She has won re-election easily in the past and was expected to do so again if she sought another term next year.

A strong liberal voice for women, seniors, and the environment, Mikulski became the longest-serving woman in the history of Congress in 2012. She was first elected to the House of Representatives in 1976 and has served in the Senate since 1987.

When Mikulski was first elected there was only one other woman in the Senate; now there are 20. For years she has been a mentor and role model to other female senators, Republican and Democrat, and is even credited with getting rid of the chamber's requirement that women wear skirts on the Senate floor.

"When Sen. Mikulski decided that she was going to wear pants while casting her votes, it was the rule that had to change, not her," said Sen. Patty Murray, D-Wash., a protege. "She fought for us before we even got here, walked into rooms women had not been welcome in before, and made sure to keep her foot stuck in the door."

President Barack Obama lauded Mikulski in a statement as an institution and an inspiration.

Mikulski said Monday that when her term has ended, "I will know that I will have given it my best shot."

"I want the people of Maryland to know there's nothing gloomy about this announcement," she added. "There's no health problem. I'm not frustrated with the Senate."

She becomes the second Senate Democratic woman to announce her retirement this year, following Barbara Boxer of California.

In a 2014 interview, Mikulski said her approach as chair of the Appropriations panel was "to focus with civility and courtesy. Old school values. Don't do surprises or stunts and negotiate directly and not through the press."

Senate Republican Leader Mitch McConnell described Mikulski at the time as forceful and results-oriented. "I think she's terrific," he said.

She spent decades honing relationships with members of both parties, learning their needs and end goals. After a short tenure as chairman, she now is the top Democrat on the panel after Republicans captured control of the Senate in last November's elections.

Mikulski has also been an active advocate of equal pay for women. She sponsored legislation last year aimed at tightening a 1963 law that made it illegal to pay women less than men for comparable jobs because of their gender. But Senate Republicans blocked the bill in an April 2014 floor showdown.

"When I hear all these phony reasons, some are mean and some are meaningless, I do get emotional," Mikulski said of arguments against the legislation. "I get angry. I get outraged. I get volcanic."

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AP Special Correspondent David Espo and writers Donna Cassata and Laurie Kellman contributed to this story. Werner reported from Washington.