So now it's Ron Paul's turn.

The diminutive Texas libertarian is poised in the latest polls to win the Iowa caucuses.

Obviously, this would be rough news for Newt Gingrich — who's in third place and falling — and very good news for Mitt Romney, who has used Michele Bachmann, Rick Perry, Herman Cain and now Paul as blockers to fend off challenges from the various "not-Mitt" candidates of the moment (Perry must feel particularly disoriented because he's been both blocker and blockee.)

And give this to Paul: He most certainly is not Mitt.

Many of Paul's defenders insist he is a champion — a lone voice, even — of the "true" Constitution and the "real" principles of the conservative movement. Moreover, they are determined to tell you that, often in emails written in ALL CAPS.

For the record, I like many of Paul's positions on the role of the federal government. I find it charming that he's making a big issue about the freedom to drink raw milk. I don't believe his positions on states' rights are racist. I think he goes way too far on the Federal Reserve. He sometimes sounds like he thinks Fed Chairman Ben Bernanke is sapping our precious bodily fluids. But he's also been prescient about the Fed's unchecked power.

Or maybe it wasn't prescience. Maybe it was paranoia. After all, if you worry about enough things, some of them are going to turn out to be accurate. When a hypochondriac is finally diagnosed with a disease after years of pointless worrying, it kind of takes the bite out of his I-told-you-sos.

This is the point in the standard anti-Ron Paul column where I am supposed to denounce his many bad associations, his racist newsletters — which he didn't write, he just let them go out with his name on them for years — his barmy national security ideas and his potted history of American foreign policy. And, should Paul go on to be a serious contender for the Republican nomination, I reserve my right to revisit all of that because — contrary to the claims of many of his supporters — Paul's background hasn't been scrutinized nearly enough.

But rather than get into all that, let's take the idea of a President Paul as seriously as his supporters say we should — though the idea he could beat Obama in the general election strikes me as crazier than Joe Biden on angel dust.

Paul routinely says that he's the only candidate who promises real change. For instance, he proposes cutting $1 trillion from the budget in the first year of his presidency. Now, show of hands: Who thinks Ron Paul could get those kinds of cuts through Congress? Anyone? OK, anyone who also believes the Council on Foreign Relations is a secret cabal determined to create a North American super-state?

I thought so.

I like, even love, many of Paul's proposals: turning Medicaid into block grants, getting rid of the Department of Education, etc. But he's not the man to get them accomplished, largely because the president doesn't have unilateral authority.

"It's ironic that the only way the libertarian-pure-constitutionalist in the race could do the things he's promising is by using powers not in the Constitution." --Jonah GoldbergPresidential power is the power to persuade — Congress, the media and ultimately and most important, the American people. The power of the purse, meanwhile, resides on the other end of Pennsylvania Avenue.

Paul has been in Congress, off and on, for nearly 30 years. In that time, he will rightly tell you, Congress has spent money with reckless abandon, expanded the state's police powers, launched numerous wars without a declaration of war and further embraced fiat money (he got into politics when Richard Nixon took us fully off the gold standard). During all of that, he took to the floor and delivered passionate speeches in protest convincing … nobody.

Paul's supporters love to talk about how he was a lone voice of dissent. They never explain why he was alone in his dissent. Why couldn't he convince even his ideologically sympathetic colleagues? Why is there no Ron Paul caucus?

Now he insists that everyone in Washington will suddenly do what he wants once he's in the White House. That's almost painfully naïve. And it's ironic that the only way the libertarian-pure-constitutionalist in the race could do the things he's promising is by using powers not in the Constitution.

Jonah Goldberg is a visiting fellow at AEI.