WASHINGTON—The start of a new Democratic-led House this year also marked the end of an era, as the House Republican caucus now doesn’t have a single lawmaker considered a supporter of abortion rights.

The unanimity on opposing abortion rights followed the retirements of centrist Republican Reps. Charlie Dent of Pennsylvania and Rodney Frelinghuysen of New Jersey. Their ranks could continue to diminish in the Senate, where only GOP Sens. Lisa Murkowski of Alaska and Susan Collins of Maine remain as supporters of abortion rights.

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