If you want to understand why Paul Ryan isn’t running for reelection and will leave Congress at the end of the year instead, don’t think about his Democratic challenger, Randy Bryce (a.k.a. “IronStache”). Think about his erstwhile Republican primary opponent, Paul Nehlen.

Nehlen ran against Ryan for not disliking foreigners enough. He asked Ryan to debate him on a proposal to deport all Muslim Americans from the US. He once showed up at Ryan’s house with a group of women whose children had been killed by unauthorized immigrants. After his 2016 defeat, Nehlen got deeper and deeper into white nationalism — these days, he can usually be found posting pro-Trump, anti-Semitic memes on the alt-right social network Gab.

Nehlen was never a threat to beat Ryan. Ryan walloped him in 2016 and was never in serious danger of losing to him in 2018, as far as anyone could tell. But Nehlen’s existence was fundamentally a reminder that a large part of the party Ryan was trying to lead didn’t trust him and didn’t agree with him about what the Republican Party should be. And even if that faction wasn’t going to unseat him in his own district, it’s won the party.

Paul Ryan is a small-government ideologue in a Republican Party that increasingly sees small-government ideology as a tool of identity politics, rather than the other way around. There’s nothing here for him anymore.

Paul Ryan was elected speaker on the promise to avoid immigration. Then came Donald Trump.

Paul Ryan didn’t really seek out the speaker position. When John Boehner left in 2015, it became clear that no one else could win the support of run-of-the-mill House Republicans without being torched by the hardline Freedom Caucus. Ryan spent days refusing to take the gig, and then, finally, acquiesced.

But even though Ryan was the only mainstream Republican the Freedom Caucus trusted even a little, they didn’t trust him unreservedly. Conservatives were deeply worried about his past support for comprehensive immigration reform, including legalization for unauthorized immigrants currently in the US. To become speaker, Ryan promised the Freedom Caucus that he wouldn’t make any sudden moves on immigration by aligning with Democrats over conservatives — that he’d adhere to the Hastert Rule (only bringing bills to the floor if they’re supported by a majority of Republicans) on any immigration bills.

The easiest way to keep this promise was to not bring any immigration bills to the House floor at all, and to try to avoid making any policy promises one way or the other. As speaker, Ryan made a couple of reassuring-sounding comments to unauthorized immigrants worried about their fates under Trump. Before Trump’s inauguration, he told one immigrant protected under the Deferred Action for Childhood Arrivals program that she was safe from deportation; after the Trump administration announced it was ending the DACA program, Ryan told its recipients to “rest easy” because Congress would pass a bill to protect them in the coming months.

But Ryan never made any promises, much less backed any bills to legalize DACA recipients or other immigrants. He never spent any political capital. He did nothing that could possibly be construed as a violation of his promise to the Freedom Caucus.

Increasingly, though, not moving bills that immigration hawks would dislike isn’t sufficient. The White House is increasingly frustrated that Congress won’t do more to pass immigration bills the White House wants — to end “catch and release” by tightening asylum laws, pass sweeping restrictions on legal immigration, and give Trump billions of dollars for his wall on the US-Mexico border.

None of these are things Paul Ryan is passionate about. If anything, like many Republicans, he supports keeping legal immigration at or near current levels (even if he wants to shift who those immigrants are), and he’s skeptical of multibillion-dollar government spending projects.

To pass any bill — especially one on a contentious issue — Ryan would have to spend political capital to advance someone else’s agenda. If he refused, he could lose the White House — and White House loyalists within his own conference.

Donald Trump’s Republican Party cares less about passing bills than about fighting the culture war

Of course, Ryan managed to survive under Trump for a year, and under a Trump-led GOP for basically his entire speakership. It was possible, if the reward was worth it.

But what’s left for Ryan, and for other conservatives who believe the purpose and size of the federal government is the defining question of our time? They have passed a multibillion-dollar tax cut — only to see the president threaten the confidence of business owners with an escalating trade war. They don’t appear to have any prospects of overhauling Medicare over the veto of a president who explicitly promised to protect it, or overhauling Social Security on behalf of a base that is increasingly of Social Security-eligible age.

Oversight of government is no longer primarily a way to cut down on waste, fraud, and abuse. It’s now a way to protect the president from an untrustworthy “deep state.” There’s no longer any appeal in protecting “the rule of law” for the purposes of fighting unauthorized immigration; the concern is that foreign countries are sending foreign people, legally and illegally, for nefarious ends.

The answer to the question of “What is the Republican Party?” has changed. It’s no longer a political organization dedicated to shrinking government and protecting the free market. It’s now one side of an ongoing culture war — for immigration agents and against immigrants, for police officers and against disruptive (black) protesters, for the White House and against the “deep state.” It’s not exclusively a white identity politics, but without race, it’s hard to imagine the bonds that tie Donald Trump to the Republican base.

A decade ago, some pundits like Thomas Frank speculated that Republican voters were being duped: They voted for politicians on cultural issues, but the politicians were more interested in economic policies that would hurt their own base. In the age of Trump, the tables have turned. A Republican president, cheered on by the Republican base, is more interested in waging an ongoing culture war — against everyone from NFL players to FBI agents — than in any particular policy. And even if not every elected Republican is enthusiastically on board, the ones who aren’t are now on the defensive.

Why would Ryan want to lead such a party? What’s in it for him? What would he get out of it? The only obvious answer to this question would be to fight for his vision of the party. That appears not to be a fight Paul Ryan wants to have.