The GOP’s inability to scrap ObamaCare this week means, among other things, that President Trump will end his first six months in office without a major legislative accomplishment. And one question is how much his supporters care.

Recent Wall Street Journal/NBC News polling gives the president a 40% job-approval rating among all voters, while 55% disapprove. In counties Mr. Trump won last year, however, voters still back him by 50% to 46%. Similar results come from a Washington Post/ABC News survey released Sunday, which found...