It’s not exactly a shocking revelation that John McCain’s budget numbers don’t add up. Presidential candidates’ numbers are often rather pie-in-the-sky, and political observers have been conditioned to give campaigns at least a little leeway and wiggle room.

But from time to time, it’s worth keeping in mind that McCain’s budget promises aren’t just wrong, they’re spectacularly ridiculous.

McCain recently told NPR, for example, “I can eliminate $100 billion of wasteful and earmark spending immediately — $35 billion in big spending bills in the last two years, and another $65 billion that has already been made a permanent part of the budget.” He told George Stephanopoulos almost the exact same thing: “You do away with those, there’s $100 billion right before you look at any agency.”

This magical savings, McCain has said, allows him to make promises about eliminating the deficit altogether in four years, and making Bush’s tax cuts permanent, and passing new tax cuts of his own, and keeping U.S. troops in Iraq indefinitely.

The WaPo’s Michael Dobbs took a closer look at McCain’s inability to do arithmetic.

What's more, looking at the NPR quote, McCain said $65 billion in earmark spending “has already been made a permanent part of the budget.” No one knows what on earth that even means — Bruce Riedl, a budget analyst with the conservative Heritage Foundation, told Dobbs, “I don’t understand how they come up with that.”

Excluding those programs McCain has promised to preserve, the draconian slashing of earmark expenditures might save around $10 billion a year. But that is still a long way from the $100 billion in savings that McCain says that he can identify “immediately.”

The McCain camp now says that the senator never meant to suggest that his proposed $100 billion in savings would all come from earmarks. Holtz-Eakin told me that McCain had simply promised to cut overall spending by around $100 billion. Some of these savings will come from earmarks, some from other parts of the budget. He declined to identify which specific projects would be cut.

Asked whether McCain had misspoke or whether he had been misunderstood in his focus on eliminating earmarks, Holtz-Eakin replied: “a bit of both.”

Dobbs concluded, “To use a phrase coined by George H.W. Bush, this is ‘voodoo economics,’ based more on wishful thinking than on hard data or carefully considered policy proposals.”

In the broader political context, maybe reporters and voters expect candidates to lie when making budget promises, but McCain has vowed to be different — more honest, more forthcoming, less deceptive. He’s been in Congress for a quarter of a century. He knows the budget, he knows what’s possible, and yet, he tries to deceive voters anyway.

If McCain is already lying about what he can achieve with the budget, how can anyone take him seriously on anything else?