Last week, a zombie went to New Hampshire and staked its claim to the Republican presidential nomination. Well, O.K., it was actually Gov. Chris Christie of New Jersey. But it’s pretty much the same thing.

You see, Mr. Christie gave a speech in which he tried to position himself as a tough-minded fiscal realist. In fact, however, his supposedly tough-minded policy idea was a classic zombie — an idea that should have died long ago in the face of evidence that undermines its basic premise, but somehow just keeps shambling along.

But let us not be too harsh on Mr. Christie. A deep attachment to long-refuted ideas seems to be required of all prominent Republicans. Whoever finally gets the nomination for 2016 will have multiple zombies as his running mates.

Start with Mr. Christie, who thought he was being smart and brave by proposing that we raise the age of eligibility for both Social Security and Medicare to 69. Doesn’t this make sense now that Americans are living longer?

No, it doesn’t. This whole line of argument should have died in 2007, when the Social Security Administration issued a report showing that almost all the rise in life expectancy has taken place among the affluent. The bottom half of workers, who are precisely the Americans who rely on Social Security most, have seen their life expectancy at age 65 rise only a bit more than a year since the 1970s. Furthermore, while lawyers and politicians may consider working into their late 60s no hardship, things look somewhat different to ordinary workers, many of whom still have to perform manual labor.

And while raising the retirement age would impose a great deal of hardship, it would save remarkably little money. In fact, a 2013 report from the Congressional Budget Office found that raising the Medicare age would save almost no money at all.

But Mr. Christie — like Jeb Bush, who quickly echoed his proposal — evidently knows none of this. The zombie ideas have eaten his brain.

And there are plenty of other zombies out there. Consider, for example, the zombification of the debate over health reform.

Before the Affordable Care Act went fully into effect, conservatives made a series of dire predictions about what would happen when it did. It would actually reduce the number of Americans with health insurance; it would lead to “rate shock,” as premiums soared; it would cost the government far more than projected, and blow up the deficit; it would be a huge job-destroyer.

In reality, the act has produced a dramatic drop in the number of uninsured adults; premiums have grown much more slowly than in the years before reform; the law’s cost is coming in well below projections; and 2014, the first year of full implementation, also had the best job growth since 1999.

So how has this changed the discourse? On the right, not at all. As far as I can tell, every prominent Republican talks about Obamacare as if all the predicted disasters have, in fact, come to pass.

Finally, one of the interesting political developments of this election cycle has been the triumphant return of voodoo economics, the “supply-side” claim that tax cuts for the rich stimulate the economy so much that they pay for themselves.

In the real world, this doctrine has an unblemished record of failure. Despite confident right-wing predictions of doom, neither the Clinton tax increase of 1993 nor the Obama tax increase of 2013 killed the economy (far from it), while the “Bush boom” that followed the tax cuts of 2001 and 2003 was unimpressive even before it ended in financial crisis. Kansas, whose governor promised a “real live experiment” that would prove supply-side doctrine right, has failed even to match the growth of neighboring states.

In the world of Republican politics, however, voodoo’s grip has never been stronger. Would-be presidential candidates must audition in front of prominent supply-siders to prove their fealty to failed doctrine. Tax proposals like Marco Rubio’s would create a giant hole in the budget, then claim that this hole would be filled by a miraculous economic upsurge. Supply-side economics, it’s now clear, is the ultimate zombie: no amount of evidence or logic can kill it.

So why has the Republican Party experienced a zombie apocalypse? One reason, surely, is the fact that most Republican politicians represent states or districts that will never, ever vote for a Democrat, so the only thing they fear is a challenge from the far right. Another is the need to tell Big Money what it wants to hear: a candidate saying anything realistic about Obamacare or tax cuts won’t survive the Sheldon Adelson/Koch brothers primary.

Whatever the reasons, the result is clear. Pundits will try to pretend that we’re having a serious policy debate, but, as far as issues go, 2016 is already set up to be the election of the living dead.