Governor Charlie Baker of Massachusetts and his lieutenant governor, Karyn Polito, announced this month that they would not seek re-election in 2022. It's another nail in the coffin of moderate Northeastern Republicanism. That used to be a significant strand within the Republican Party, but it is increasingly rare. Mr. Baker and Ms. Polito were among the few remaining exceptions. Their impending departure tells a political story with implications beyond the Bay State. Even the northeastern...
