When the obituary for the Republican Party is written, the year 1980 will be cited as the beginning of the end. Reaganism was in full flower, but the big tent was already folding. Republican leaders endorsed a constitutional ban on abortion at the convention that summer, ending the party’s historic commitment to women’s rights and personal freedom.

“We are about to bury the rights of over 100 million American women under a heap of platitudes,” protested Mary Dent Crisp, the co-chairwoman of the Republican National Committee. Her colleagues assured her that the platform was nonbinding and that reproductive health services were not in danger.

But she was prescient. As pro-choice Republicans, we refuse to support a party that has rightly earned the labels anti-woman and anti-common sense. Our organization, the Republican Majority for Choice, the organization founded by Ms. Crisp in 1988, is shutting its doors. The big tent has collapsed for good.

As Republicans, we spent four decades working inside the party to produce effective policies helping women and families. Despite growing malice from an anti-choice faction, we kept our disagreements within the family. We redoubled our efforts to find common ground, rather than simply walk away.