For decades, the idea that Iran’s regime represented the worst of the world’s worst stood as a pillar of Republican foreign policy.

But in recent months, and especially as the Trump administration has defended its preliminary peace deal, a different perspective has been taking hold in parts of the American right: Iran as a pragmatic country that the United States can, and must, learn to live with.

The stark shift has been led by President Trump, who called Iran’s leaders “strong people, smart people” last week, but it goes well beyond him. Vice President JD Vance has emerged as its main proponent. Conservatives who long had an isolationist streak have been energized. Even some longtime hawks have changed their tone.

It is too soon to say whether the change will last. Many Republicans have retained their hard-line stance, and Mr. Trump has periodically threatened to restart the war. Some of the shifting language among Republicans could be the familiar Trump-era scramble to stay aligned with a mercurial president.

But interviews show that the right-wing pivot away from traditional Republican hawkishness on Iran is driven by factors that go beyond Mr. Trump’s desire to disentangle himself from the fighting. There is a generational shift in the party away from uncompromising support for Iran’s archenemy, Israel, and even some grudging admiration for the Iranian regime’s ability to withstand weeks of fierce bombardment.

It is a domestic political dynamic with global implications — stakes made plain by the Iran war’s consequences for the energy supply of Europe and Asia and the security of the Arab countries on the Persian Gulf.