Republicans are getting their own reality check. Under Mr. Trump, a growing faction of the party was pushing isolationism, questioning alliances and trade pacts, and pressing an “America First” agenda that would have fit well in the national mood leading up to World War II, Mr. Meijer said.

In recent days, Representative Tom Cole of Oklahoma, a traditionalist Republican, sat down with the German ambassador to the United States to thank her for her country’s commitment to NATO’s defense and its aid to Ukraine.

In an interview, Mr. Cole even suggested reviving the Trans-Pacific Partnership, a landmark trade pact negotiated by President Barack Obama that would have tied together the economies of Asia, Australia, New Zealand, North America and South America to isolate China. In one of his first acts as president, Mr. Trump scuttled the agreement.

“Ukraine has got a lot of Republicans rethinking the importance of international alliances,” Mr. Cole said. “Other countries are not always a burden. They’re quite often an asset.”

For Democrats, the shift in priorities has had a price. Taking his cues from his party’s environmental wing, Mr. Biden had hoped to move the United States away from fossil fuels, blocking new leases for oil and gas exploration on federal land, opening up large swaths of ocean and land to wind and solar development, and pushing an ambitious timetable to move the country to electric cars and trucks.

Now, the fossil fuel industry is ascendant. More mainstream Democrats are using the language of Republicans, talking about an “all of the above” energy strategy that includes renewable fuels and oil and gas. Natural gas is again spoken of as a “bridge” fuel to clean energy, not an enemy of the planet.

“Some of my colleagues are presenting a false choice,” said Representative Josh Gottheimer of New Jersey, a leading voice of centrist Democrats. “You can be for alternative energy and energy independence with aggressive, long-term goals, and be for fully tapping our domestic energy resources.”