But we have a lot of evidence about how private-sector competition in health insurance works, and it’s not favorable. The individual insurance market, which comes closest to the conservative ideal of free competition, has huge administrative costs and has no demonstrated ability to reduce other costs. Medicare Advantage, which allows Medicare beneficiaries to buy private insurance instead of having Medicare pay bills directly, has consistently had higher costs than the traditional program.

And the international evidence accords with U.S. experience. The most efficient health care systems are integrated systems like the V.H.A.; next best are single-payer systems like Medicare; the more privatized the system, the worse it performs.

To be fair to Mr. Romney, he takes a somewhat softer line than others in his party, suggesting that the existing V.H.A. system would remain available and that traditional Medicare would remain an option. In practice, however, partial privatization would almost surely undermine the public side of these programs. For example, one problem with the V.H.A. is that its hospitals are spread too thinly across the nation; this problem would become worse if a substantial number of veterans were encouraged to opt out of the system.

So what lies behind the Republican obsession with privatization and voucherization? Ideology, of course. It’s literally a fundamental article of faith in the G.O.P. that the private sector is always better than the government, and no amount of evidence can shake that credo.

In fact, it’s hard to avoid the sense that Republicans are especially eager to dismantle government programs that act as living demonstrations that their ideology is wrong. Bloated military budgets don’t bother them much — Mr. Romney has pledged to reverse President Obama’s defense cuts, despite the fact that no such cuts have actually taken place. But successful programs like veterans’ health, Social Security and Medicare are in the crosshairs.

Which brings me to a final thought: maybe all this amounts to a case for Rick Perry. Any Republican would, if elected president, set out to undermine precisely those government programs that work best. But Mr. Perry might not remember which programs he was supposed to destroy.