New Hampshire Senator Jeanne Shaheen will not run for reelection in 2026, opening up a competitive seat and complicating Democrats’ efforts to reclaim the Senate majority.

Democratic Sen. Jeanne Shaheen of New Hampshire announced Wednesday that she will not seek reelection in 2026, a decision that will bring an end to the senator’s historic career in Congress and sets up a competitive race for the Senate seat in the Granite State.

Ms. Shaheen’s retirement will set off a high-stakes fight for an open seat in a state where she has been a leading political figure for decades.