Start with the numbers, which reveal the fault lines. The latest POLITICO Poll shows a Republican coalition divided between core MAGA voters and non-MAGA Republicans and independents who nonetheless supported Trump. Among MAGA voters, Trump remains dominant. Among non-MAGA Trump voters — the voters Republicans need to win elections — enthusiasm collapses, especially when it comes to Trump’s governing style and Trump-endorsed candidates. That alone would be a warning sign. But it’s the why behind the numbers that should worry Republicans — and especially Vance. The first fissure is foreign policy. As the Washington Post reported on Monday, Senator Ted...