U.S. Senator Jeanne Shaheen on Wednesday became the third Senate Democrat to say she would not seek reelection next year, further complicating her party's hopes of recapturing control of that chamber when President Donald Trump's term reaches its midpoint.

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.

She exemplifies integrity of the highest order,” former US Representative Ann Kuster said. “If Pappas doesn’t run, I would take a serious look at the race.”