Washington (CNN) Sen. Barbara Mikulski, the longest serving female senator in history, will retire at the end of her term.

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?"

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