Romney is the major only candidate Paul hasn't singled out in an ad. And Paul's ads against his competitors have been far more brutal than anything Romney or his super PAC have put on the airwaves. In crucial stages of the GOP primary thus far, he's put hundreds of thousands of dollars behind these ads, helping squelch Santorum and Gingrich when they posed the most danger to Romney's candidacy.

Helping Romney in his quest to make potential alternative candidates unpalatable to the conservative base is a major assist. But it's far from the only way Paul has boosted the man who ought to be his biggest nemesis -- the embodiment of the sort of soft, big-government Republicanism Paul says it's his mission to eliminate.

First there are the sins of omission -- the opportunities to criticize Romney that Paul has passed up. The liberal group ThinkProgress studied the record and found that Paul attacked other candidates 39 times in the 20 debates to date, but didn't go after Romney a single time. Even when moderators have tried to draw him into a potentially illuminating contrast with Romney, Paul has demurred. (David Gregory to Paul, Jan. 8: "Do you believe Governor Romney now when he says he is a man of constancy and that he'll stand up for conservative principles?" Paul: "You know, I think this whole discussion so far has been very superficial, and I think the question in the way that you ask it is superficial.") In some cases, Paul has even defended Romney, as in this totally unprompted swipe at Rick Perry on Sept. 7: "You know, the governor of Texas criticized the governor of Massachusetts for Romneycare, but he wrote a really fancy letter supporting Hillarycare." His attacks on all the other candidates have been gleefully vicious. But he's handled Romney with kid gloves.

That's not the only example of Paul coming proactively to Romney's aid. When Romney was under fire for his out-of-context "I like being able to fire people" sound bite in January, a "Ron Paul Campaign Statement on Republicans Attacking Capitalism" landed in reporters' inboxes. "Two important issues that should unite Republicans are a belief in free markets and an understanding that the media often use 'gotcha' tactics to discredit us," Paul campaign chairman Jesse Benton wrote in the statement. "Rather than run against Governor Romney on the issues of the day Santorum, Huntsman, and Gingrich have chosen to play along with the media elites and exploit a quote taken horribly out of context. They are also using the language of the liberal left to attack private equity and condemn capitalism in a desperate and, frankly, unsavory attempt to tear down another Republican with tactics akin to those of MoveOn.org." Romney couldn't have said it better himself.

Paul's campaign has acknowledged a policy of not going after Romney and sought to frame it as a matter of strategy. "We're not fishing from the same pond," Benton told reporters in the post-debate spin room in New Hampshire, meaning there's no overlap between potential Paul voters -- young, rebellious, idealistic -- and potential Romney voters -- older, status-quo-oriented party regulars. But that's a bit of a self-fulfilling prophecy. As the two candidates most singly focused on fiscal issues and the economy, Romney and Paul could be competing for the same universe of voters not interested primarily in social issues. On the campaign trail, I have met more than one voter who claimed to be deciding between the two, like the Nevada man I encountered at a Paul rally who told me while he agreed with Paul's ideas, he planned to vote for Romney because he thought Romney could win. The upcoming Virginia primary, in which only Paul and Romney managed to get on the ballot, could test the Paul camp's theory that he wins the anti-Romney vote once Santorum and Gingrich are eliminated as choices.