What do Tucker Carlson’s announcement this week that he plans to “help build a third party” and the recent successes of candidates in Democratic primaries endorsed by the Democratic Socialists of America (DSA) have in common? Both illustrate the ways that third parties can succeed or fail in influencing politics.

In seeking to create a third party, Carlson’s aim is clear: he wants to pressure the GOP toward his view on a number of issues, whether it’s the relationship between the US government and Israel or the promotion of pro-family policies. Still, his aims are hardly similar to those of someone like Andrew Yang who wanted to build a long-term alternative to the main parties. In fact, American history is littered with parties which tended to be either single-issue or ideological projects to push the Democrats or Republicans in a particular direction on a certain policy.

Before the Civil War, the Free Soil Party was formed in opposition to slavery. In the late 19th century, meanwhile, the Populist Party was founded to advance the interests of farmers. Single-issue parties in this vein, however, tend to expire once one of the two major parties co-opts their headline issue. The Republican Party of Lincoln took on opposition to slavery, and New Deal Democrats addressed many agrarian populist grievances.

However, third parties based on a comprehensive ideology have had far more influence — but only when their members have infiltrated and captured one of the two main parties. Veterans of the Progressive Party of Robert La Follette and Theodore Roosevelt shaped the New Deal from within the Democratic coalition. Libertarians have had their greatest influence as members of the post-Reagan Republican Party, not as voters for the Libertarian Party.

Today’s democratic socialists, most notably Zohran Mamdani, are remaking the Democratic Party in their image from the inside, not through the vehicle of a third party. Populist conservatives in the Donald Trump years have failed, however, to push the Republican Party beyond its Reagan-era roots from within. Should Carlson attempt to do so from outside the GOP, he will likely have even less luck.

It is true that some sects within parties don’t attempt to completely redraw party policy. Since the Eighties, churchgoing white evangelicals have been the most loyal Republican voters, just as churchgoing black Protestants have been the most loyal Democratic voters. But for half a century, both have been content to outsource economic policy and foreign policy to other wings of their parties, in return for the hierarchy’s support on a few key issues — abortion, religious freedom and support for Israel for Republican evangelicals; racial equity politics for black Democrats.

In 2016, and again in 2024, Trump seemed poised to replace his party’s libertarian-evangelical alliance with a new populist Republican coalition that was less interventionist in foreign policy and pro-worker. But in his two terms, Trump has governed mostly on behalf of the old Bush-era alliance of libertarians and Christian Zionist evangelicals. He has given the Christian Zionists everything they wanted — moving the US embassy to Jerusalem, endorsing the ethnic cleansing of Gaza and its conversion into a resort development, and going to war twice with Iran at the behest of the Israeli regime. This will surely be an indication to Carlson that policy does not radically change when someone attempts to operate within the GOP.

On the Left, the ascendant progressives are flexing their muscle against the old Democratic establishment. Carlson seeks to do the same on the back of Right-populist opposition to Israel and war in the Middle East, yet support for Trump’s Israel policy comes largely from the very same evangelical Christian Zionists who remain the Republican Party’s most loyal and powerful electoral voting bloc, not American Jews.

Lacking the organizational skill, resources and fervor of the DSA and the larger progressive coalition, any conservative populist third-party movement, led by Carlson or anyone else, is likely to crash and burn if it gets off the ground at all. The failure of a populist realignment to appear under Trump means that the energetic Democratic Party alliance of college-educated progressives and immigrants, which formed in the 2010s, will face the decaying Bush-era alliance of pro-business libertarians and Christian Zionist evangelicals that clings to power despite its unpopularity. This settlement looks unlikely to change in the coming years.