WASHINGTON — President-elect Donald J. Trump will enter the White House having promised to radically alter United States foreign policy, with ramifications for Americans and the world.

But it’s not yet clear how. Mr. Trump offered vague and sometimes contradictory proposals during his campaign, with few of the typical details or white papers. Voters, foreign policy professionals and the country’s allies are all, to a real extent, left guessing.

Here, then, is a rundown of what we know about Mr. Trump’s foreign policy ideas and what some experts say about their feasibility and likely ramifications.

What are Mr. Trump’s proposed policies?

Mr. Trump has repeatedly emphasized a set of ideas that would reduce America’s role in the world. He said he would take unilateral action, move away from traditional allies and move closer to adversaries.