The long decline of the Republican Party’s internationalist wing may have reached a tipping point. Since Donald Trump emerged as the GOP’s dominant figure in 2016, he has championed an isolationist and nationalist agenda that is dubious of international alliances, scornful of free trade, and hostile to not only illegal but also legal immigration. His four years in the White House marked a shift in the party’s internal balance of power away from the internationalist perspective that had dominated every Republican presidency from Dwight Eisenhower through George W. Bush. But even so, during Trump’s four years in office, a substantial remnant of traditionally internationalist Republicans in Congress and in the key national-security positions of his own administration resisted his efforts to unravel America’s traditional alliances. Now though, evidence is rapidly accumulating on multiple fronts that the internal GOP resistance is crumbling to Trump’s determination to steer America away from its traditional role as a global leader. In Congress, that shift was evident in last week’s widespread Senate and House Republican opposition to continued aid for …