On Monday, I wrote about the "the policy gap" between Barack Obama and Mitt Romney. If you missed it, the policy gap, put simply, is this: Obama has proposed policies. Mitt Romney hasn’t. Rather, Romney has proposed simulacra of policies: They look like policies from far away, but the closer you get, the less there is. As Romney told CNBC in response to an early effort to estimate the cost and consequences of his tax plan, “I think it’s kind of interesting for the groups to try and score it because frankly it can’t be scored." That Romney thought this was a devastating rebuttal to the analyses of his plan, as opposed to a devastating admission as to the hollowness of his "plan," was telling.

But it's not just the gap between the two candidates that astonishes. Romney's vagueness is unique among modern presidential campaigns. He's released far fewer policy details than John McCain or Barack Obama in 2008, or George W. Bush in 2000. The question is why.

It's not Romney's personality. Romney is, by all accounts, a detail-oriented policy wonk. This is, in fact, the whole argument for Romney: He may not be able to feel your pain, but he can balance your budget. Most everyone who has ever worked with or for him comments on his vast appetite for data and his pragmatic approach to governing. Which leads to a possible explanation for the policy gap: Where Bush and McCain and Obama had to release specific policy proposals to answer concerns that they were insufficiently informed on the details of policy, Romney is using his reputation for technocratic diligence as an excuse for refusing to release specific policy proposals.

But another, and perhaps more relevant, theme from Romney's past is his tendency to choose policy positions based on a strategic analysis of his next campaign. In 'The Real Romney,' Michael Kranish and Scott Helman quote a former Romney aide who says his boss's approach to policy was that "everything could always be tweaked, reshaped, fixed, addressed. It was foreign to him on policy issues that core principles mattered -- that somebody would go back and say, 'Well, three years ago, you said this.'"

When Romney ran for Senate in 1994, he portrayed himself as a moderate Republican. In 2002, he said, "my views are progressive." When he began planning a run for president after the 2004 election, he saw that the front-runners for the Republican nomination, John McCain and Rudy Giuliani, were mistrusted by social conservatives, and so the formerly pro-choice, pro-gay rights governor remade himself as a social conservative. So far, in 2012, he has run a campaign de-emphasizing the social conservatism that was at the core of his 2008 campaign and elevating economic policy.

But Romney's talent for strategic positioning has, in this campaign, placed him between some very difficult crosscurrents. In recent years, the Republican Party has moved so far and fast to the right that their policy apparatus hasn't been able to keep up, and much of what they want -- tax cuts for the rich combined with deep cuts to Medicare, for instance -- would horrify swing voters. Simultaneously, the Democratic Party has embraced a number of proposals that were previously associated with, well, Mitt Romney, rendering a number of once-uncontroversial plans radioactive on the right. These dynamics have pushed Romney into a kind of forced incoherence, where the only way to obscure the problems in the policy proposals the Republican base will accept is to hollow out the details that would permit them to be understood. A few examples.

Taxes. It's mostly forgotten now, but Romney's initial tax plan was relatively modest. You can see it in his original economic plan. He called for the extension of the Bush tax cuts, and the elimination of taxes on investment income for people making less than $250,000 a year. But then Herman Cain caught fire with his 9-9-9 plan, and Newt Gingrich and Rick Santorum came out with even larger tax cuts, and the Romney campaign began falling behind in the polls. So they unveiled a far larger tax cut. But because Romney, unlike Gingrich or Cain, had to take seriously the possibility that he'd make it past Super Tuesday, he had to make assurances to moderate voters that the plan wouldn't increase the deficit or shift the tax burden to the poor. The problem is that there's no way to make the math of these promises work. And so the Romney campaign has simply withheld the details that would make clear which promises they're breaking.

You can see the Massachusetts health-care law on Romney's left, directly in front of the picture of Ann Romney.

Health care. In Mitt Romney's official portrait commemorating his governorship of Massachusetts, there are three items on the desk. A lamp, because he does not have night vision. A picture of Ann Romney, because he is married to her. And a copy of his health-reform law, because that was his signature achievement as governor. The problem is that that law proved so appealing that Barack Obama and the Democrats used them as the basis for their health-care reforms in 2009. And Republicans hate those health-care reforms. So Romney has tried to walk a fine line: He has agreed that his health-care reforms would be a terrible idea nationally, but he has continued to argue that they were a great idea for Massachusetts. It's thus no surprise that Romney's health-care plan is vague: He still believes in the analysis that led to his 2005 plan. He just can't say so.

Financial regulation. Romney's problem in this area is simple. Republicans -- and the public -- don't like the banks. But the banks like Romney. His top contributor is Goldman Sachs. In second place is JP Morgan Chase and Co. Then comes Morgan Stanley. And then Bank of America. Fully eight of Romney's top 10 contributors are banks. Which puts Romney in a tough position. The main Republican critique of Obama's Dodd-Frank reforms is that they didn't go far enough. Some conservative intellectuals, in fact, have begun arguing that we should simply break up the big banks altogether. But the big banks don't want to be broken up, and they're not going to continue contributing to the campaign of the guy who wants to break them up. What these two sides do agree on is that they hate Dodd-Frank and want it replaced with...something. And so Romney's position is that he will repeal Dodd-Frank and replace it with...something.

Spending. If there's one policy that exists as a Republican litmus test, it's Paul Ryan's budget. And so Romney has been very clear: He supports Paul Ryan's budget. But if there's one policy with the potential to scare swing voters, it's Paul Ryan's budget. And so Romney's campaign has been very clear: He doesn't support all the cuts in Paul Ryan's budget, and he particularly opposes the unpopular cuts to Medicare. Again, Romney is trying to walk a very fine line: Signal enough support for Ryan's budget to calm conservatives, but telegraph sufficient qualms with it to keep Ryan's budget from becoming Romney's budget.

Romney adopted these policies during the primary campaign. The idea, perhaps, was that they could always be tweaked, reshaped, fixed, addressed. As Eric Fehrnstrom, Romney's top communications guru famously said, ""I think you hit a reset button for the fall campaign. Everything changes. It's almost like an Etch A Sketch — you can kind of shake it up and we start all over again."

But that hasn't proven true. Since effectively securing the nomination, Romney has not moved to the center in any visible way. Having taken these positions, he is now lashed to them. That's meant his only hope has been keeping voters from really understanding what it is that he's proposing. And the easiest way to do that has been to omit the details that would make clear what he's proposing. Thus, the policy gap.

Perhaps the bigger question, however, is what happens if Romney is elected president. Here too the idea is likely that his promises can be tweaked, reshaped, fixed, addressed. Recall Barack Obama opposing the individual mandate during the 2008 campaign only to endorse it as president. But while presidents do betray campaign rhetoric, the evidence is clear that they typically try to keep their campaign promises. And Romney is likely to be in a worse position than most if he tries to break them.

The odds are that if Romney wins, he will have a Republican Congress that doesn't much trust him. That means he won't be able to blame reversals on the need to strike a deal with congressional Democrats, and he won't be working with a Republican majority inclined to support his agenda rather than their own. And so a policy agenda that Romney purposefully kept vague because it would be too unpopular and difficult to explain will be a policy agenda that Romney might be forced to hew to as president.