Mr. McCain’s lingering reputation as a maverick straight talker comes largely from his opposition to the Bush tax cuts of 2001 and 2003, which he said at the time were too big and too skewed to the rich. Those objections would seem to have even more force now, with America facing the costs of an expensive war  which Mr. McCain fervently supports  and with income inequality reaching new heights.

But Mr. McCain now says that he supports making the Bush tax cuts permanent. Not only that: he’s become a convert to crude supply-side economics, claiming that cutting taxes actually increases revenues. That’s an assertion even Bush administration officials concede is false.

Oh, and what about his earlier opposition to tax cuts? Mr. McCain now says he opposed the Bush tax cuts only because they weren’t offset by spending cuts.

Aside from the logical problem here  if tax cuts increase revenue, why do they need to be offset?  even a cursory look at what Mr. McCain said at the time shows that he’s trying to rewrite history: he actually attacked the Bush tax cuts from the left, not the right. But he has clearly decided that it’s better to fib about his record than admit that he wasn’t always a rock-solid economic conservative.

So what does the conversion of Mr. McCain into an avowed believer in voodoo economics  and the comparable conversions of Mitt Romney and Rudy Giuliani  tell us? That bitter partisanship and political polarization aren’t going away anytime soon.

There’s a fantasy, widely held inside the Beltway, that men and women of good will from both parties can be brought together to hammer out bipartisan solutions to the nation’s problems.

If such a thing were possible, Mr. McCain, Mr. Romney and Mr. Giuliani  a self-proclaimed maverick, the former governor of a liberal state and the former mayor of an equally liberal city  would seem like the kind of men Democrats could deal with. (O.K., maybe not Mr. Giuliani.) In fact, however, it’s not possible, not given the nature of today’s Republican Party, which has turned men like Mr. McCain and Mr. Romney into hard-line ideologues. On economics, and on much else, there is no common ground between the parties.