Former Fox News host Tucker Carlson and former Republican representative Marjorie Taylor Greene – once among Donald Trump’s most prominent champions – announced recently that they have left the Republican party.

Both rightwing superstars had feuded with the president throughout his second term, but their split was provoked by Trump’s war with Iran and what they viewed as his elevation of foreign affairs over domestic concerns like inflation and high gas prices. Although both have said that they will not support Democrats, their defection points to serious divisions within the Republican party that could weaken its prospects in the midterm elections and beyond.

The Republican establishment has dismissed the pair as malcontents and Trump has reviled them with his usual insults, calling Greene a traitor and Carlson a “low-IQ person”.

Other conservative commentators have claimed their critique stems from animus against Israel. Greene was the first Republican member of Congress to refer to Israel’s actions in Gaza as a “genocide”, and Carlson has charged that Trump betrayed the American people by allowing Israel to push him into going to war with Iran.

Carlson’s criticism of Israel, coming on the heels of his softball interview with the white nationalist influencer Nick Fuentes, has provoked accusations of antisemitism that he has denied.

Although Greene’s loopiness makes it difficult to take her seriously – who can forget her fulminations against “Nancy Pelosi’s gazpacho police”? – both Greene and Carlson merit consideration as potential 2028 presidential contenders. Their political strength lies in their influence with the “America first” faction of the Republican party, as opposed to the Maga faction dominated by Trump. Although Trump was long able to keep both factions in coalition, they represent different worldviews that correspond to different historical incarnations of American conservatism.

The America First Committee was the leading pressure group in 1940-1941 campaigning against US entry into the war in Europe. Although it began as a nonpartisan movement, “America first” became associated with populist nationalism and the antisemitism of spokespeople like Charles Lindbergh.

Trump, in reviving the “America first” label for his 2016 campaign, drew upon a deep and persistent strand in American political culture that fears becoming entangled in other countries’ wars and grievances, views immigrants with suspicion and hostility, and distrusts internationalist foreign policy as a project that benefits elites instead of the American people. Carlson, who has articulated the position of “America first” conservatives in terms that would have been recognizable to mid-20th-century isolationists like Senator Robert Taft, understandably feels betrayed by Trump’s decision to go to war against Iran.

But Trump’s most resonant political slogan – “Make America great again” – looks back to different eras of conservatism from pre-second world war isolationism. Trump rarely defines when exactly he believes America experienced the greatness he has promised to recapture.

But when pushed he invokes, first, the period of American military and industrial expansion in the late 19th and early 20th centuries, and second, the decades after the end of the second world war when baby boomers like Trump himself were born.

Trump’s Maga supporters have expressed nostalgia for America’s Gilded Age, when the country’s booming industrial base was largely protected from foreign competition and tariffs were the primary source of revenue for the federal government. But the late 19th century also marked the onset of American imperialism, with the annexation of the Philippines after the Spanish-American war – an action applauded by Rudyard Kipling in his 1899 poem Take Up the White Man’s Burden. Trump believes that a strong nation should dominate weaker ones and take whatever resources and territory it requires for its own greatness.

Trump’s “Donroe Doctrine” echoes the 19th-century Monroe Doctrine’s claim to US regional hegemony, and his siding with Russia against Ukraine harkens back to that era’s belief that great powers could keep the peace by respecting each other’s spheres of influence. Trump shares the America firsters’ contempt for alliances and US global responsibilities. But Maga is not an isolationist creed, as Trump’s actions in Venezuela and Iran have demonstrated.

The 1950s is the decade that marks America’s vanished utopia in the minds of many Maga supporters. In fact, a 2024 survey found that about 70% of Republicans think that America’s culture and way of life have changed for the worse since the 1950s, as compared with only 30% of Democrats who say the same.

Republicans from both the Maga and “America first” factions express nostalgia for what they consider to have been a time of patriotism, religiosity and growing prosperity for blue-collar breadwinners. Their critics, unsurprisingly, charge that they want to return America to an era when minorities were largely invisible, gays and lesbians were in the closet and women’s possibilities were mostly restricted to marriage and childbearing. But Trump also relishes the memory of a time when America was by far the most powerful nation and wasn’t shy about using its power to order the world to its liking – which again hardly describes the isolationist vision of “America first”.

“I never understood it,” Carlson said of Maga in a recent podcast interview. “I think there was a strong latent desire in the hearts of a lot of Americans to improve the country … but it was imprecise by design.” Trump’s charismatic incoherence – and the restraining influence of his more traditionally Republican advisers during his first term – allowed him to paper over the contradictions between Maga and “America first”. But it’s unlikely that any other 2028 Republican presidential candidate – and certainly not JD Vance – will be able to hold these factions together with anything like Trump’s success.

“I’ve been a consistent defender for 35 years of the Republican party,” Carlson told his interviewers. “And if I’m out, then I think a lot of other people are out.” Disillusioned America firsters may sit out the midterm elections, particularly if instability in the Middle East continues to be a drag on the economy.

It’s not impossible to imagine Carlson or Greene attempting to retake control of the Republican party in 2028, or even creating some kind of populist-isolationist third party. But it’s also quite conceivable that shared hatred of the left will continue to keep Republicans together despite their factional disagreements.

• Geoffrey Kabaservice is the director of political studies at the Niskanen Center in Washington, as well as the author of Rule and Ruin: The Downfall of Moderation and the Destruction of the Republican Party