Republicans may or may not be days away from passing a politically toxic bill to cut taxes for the rich and health care for the poor, and as they’ve pressed ahead against public opinion, the public interest, and (at times, it seems) their own better judgment, even sophisticated political analysts have asked: why? Why do they seem carried along as if by malevolent force?

Who’s this for? Who wants this? Why don’t they just … not? Couldn’t they take a beat, shelve the murder-suicide bill, renew expiring tax cuts for a couple years, and see how things look then?

There are narrow answers to these questions, but they’re pretty unsatisfying. The tax cuts are for a small number of rich people; the bill sabotages clean energy for big polluters; its tens of billions of dollars for a deportation army is for sadists like Stephen Miller. Taken altogether, it benefits a tiny, unsympathetic constituency.

What observers find so flummoxing is that Republicans lawmakers seem to lack any survival instinct. They can’t look at the sum of the bill’s provisions and see that almost everyone would be better off if they lowered their ambitions and started scratch. If they added less to the deficit; if they kicked fewer people (or ideally no people) off their health insurance.

But there’s a systemic reason they can’t help themselves.

I can’t know what will happen at the end of this effort. Perhaps it will fall apart again as it did in 2017; perhaps there aren’t enough Republican votes in one chamber or the other. But I do have a pretty good sense of why Republicans set off in this direction in the first place. It’s an old story; and if even political elites no longer understand the inertial forces at work, it’s worth retelling today.

DEFICITING PRETTY

Political scientists like to say we’re living through an era of identity-inflected, or “post-material” politics, where elected officials battle over what defines Americanness, rather than how the government ought to serve its citizens.

But for decades before Trump’s first election, the social safety net and the regulatory apparatus of the state were the gravitational center of U.S. politics: Who pays taxes, and how much, to fund what programs, for whose benefit?...