WASHINGTON — One topic has dominated conversations among elected Republicans since President Trump’s stunning victory: Will he actually pursue his campaign agenda of big-government nationalism, all but obliterating the liberal-conservative distinctions that have defined America’s political parties for a century?

While some of his advisers suggested that he would slip back into a more conventional Republican approach, Mr. Trump dropped hints in interviews, Twitter posts and other public comments that he intended to push his party away from its free-market, internationalist dogma on trade, foreign alliances, immigration, infrastructure spending and prescription drug access.

The hints are over.

An inaugural speech delivered with the same blunt force that propelled Mr. Trump’s insurgent campaign has dashed Republican hopes for a more traditional agenda. With his “new decree,” he declared himself modern America’s first populist president — and all but dared his own party to resist his Republican reformation.

“Every decision on trade, on taxes, on immigration, on foreign affairs will be made to benefit American workers and American families,” he said.