But unlike support for same-sex marriage, which rose drastically before it was legalized nationwide, Americans’ views on abortion have remained relatively consistent since 1975. A majority of Americans believe the procedure should be legal — but only in certain cases, according to Gallup’s long-running tracking poll.

Some abortion rights supporters worry that establishing abortion rights as a Democratic litmus test is too inflexible for Americans conflicted over abortion. They fear that it could hurt the party in rural areas and the more moderate, suburban districts that may hold the key to regaining the White House, and where many of the remaining vulnerable abortion clinics are.

Only five Democrats who oppose abortion rights remain in Congress, according to congressional votes tracked by NARAL, and at least two are facing primary challenges from women who have made support for abortion rights a key part of their campaign. In Louisiana, Gov. John Bel Edwards, a rare Democratic officeholder in the South, won re-election last month after campaigning on his support for a state law banning abortion after about six weeks of pregnancy.

J.D. Scholten, a Democrat running to replace Representative Steve King, an Iowa Republican, said that about 60 percent of voters in his culturally conservative district considered themselves “pro-life.”

“Where I’m from, we have a pretty big tent,” he said. “We can’t be writing off people. I need all the votes I can get.”

But many activists dispute the notion that compromise with abortion opponents constitutes a success. Appealing to the middle prioritizes the views of white moderates at the expense of the health care needs of women of color, critics like Ms. Merritt of Reproaction say.

“You have to change the structures,” she said. “We have ceded ground we didn’t need to about the power of our ideas.”