The single most important fact of Republican life in 2019 is this: The GOP is Donald Trump’s party now. When the GOP chose Trump as its presidential candidate in 2016, traditional Republican conservatives of the Buckley-Goldwater-Reagan school were forced to consider how far they might go to accommodate the ascendant nationalist-populist movement embodied by Trump. Some of them took a genuinely sympathetic view of Trump partisans who feel left behind by the elite-dominated politics of Washington and hoped to articulate a new class-solidarity synthesis on the right, while others cynically believed that they could simply redirect Trump and Trumpism to...