In a dramatic display of the new Republican order, Minnesota’s state GOP banished 18 prominent party members — including two former governors and a retired U.S. senator — as punishment for supporting a third-party candidate for governor. The stunning purge, narrowly passed by the state Republican central committee last weekend, suggests more than just a fit of pique: by banning some of the state’s leading moderates, the Minnesota GOP moved toward extinguishing a dying species of Republican in one of its last habitats. Those exiled warned that the measure, which bans the 18 former members from participating in party activities...