(Chris Carlson/AP)

But I keep running into the same reaction: Who cares? It’s a fool’s game to spend too much time analyzing campaign policy proposals. Everyone knows that politicians make all kinds of crazy promises during elections that they jettison as soon as they take office.

At least everyone thinks they know that. But it’s not true. In an article for the January/February issue of the Washington Monthly, political scientist Jonathan Bernstein argues that the evidence on this point is clear: “Presidents usually try to enact the policies they advocate during the campaign.”

We can all think of exceptions, of course. George H.W. Bush told the country to read his lips — a turn of speech that’s always confused me, incidentally; is lip-reading really so much more accurate than listening? — and then he raised taxes anyway. But such betrayals are not the rule.

Bernstein relies on two studies from the 1980s to make his point. In 1984, Michael Krukones published “Promises and Performance: Presidential Campaigns as Policy Predictors,” and found that “about 75 percent of the promises made by presidents from Woodrow Wilson through Jimmy Carter were kept.” In 1985, Jeff Fishel published “Presidents and Promises: From Campaign Pledge to Presidential Performance,” which argued “that presidents invariably attempt to carry out their promises; the main reason some pledges are not redeemed is congressional opposition, not presidential flip-flopping.”

More recent evidence supports this view, too. Politifact.com has tracked more than 500 promises Barack Obama made during the 2008 presidential campaign. It found he has kept 161, passed a compromised version of another 50, and has either been rebuffed by Congress or is making progress toward another 239. In only 56 cases — about 10 percent — has Obama actually broken a promise, and in the biggest of those cases — ending the Bush tax cuts for families making more than $250,000 — there’s a good chance the promise will be kept when the tax cuts expire at the end of this year.

Even the elder Bush’s famed betrayal on taxes shows the importance of campaign promises. Bush, who was dealing with large deficits created, in part, by tax cuts passed by his predecessor, tried mightily to balance the budget using spending cuts. But Bush wasn’t a dictator, and Congress was controlled by Democrats. So Bush eventually compromised.

Reasonable people disagree about whether the conservative backlash to Bush’s compromise was a significant factor in his 1992 loss. But it certainly didn’t help. And the resulting suspicion among conservatives that anti-tax politicians would renege on their campaign promises led to Grover Norquist’s anti-tax pledge, a highly effective enforcement device. Bush’s betrayal, in other words, was swiftly punished by his base and led to more effective policing of Republican politicians. It turns out that “Read my Lips” isn’t evidence that politicians don’t keep their campaign promises. It’s one of many reasons that they do.

Bernstein speculates that the public believes politicians routinely backtrack because promises that are betrayed “get a lot more attention than do the ones that are redeemed, which often can seem by the time they are finally acted on as foregone conclusions, not news.” That’s likely part of it. Another part, I think, is that the public conflates “promises that are broken” with “promises that are not kept.” Presidents support all kinds of policies that Congress ignores, opposes or modifies. As a result, presidents routinely overpromise and under-deliver. But the fact remains: Presidents at least try to deliver on the vast majority of their campaign promises.

In fact, it’s worth asking why presidents don’t backtrack on their promises more often. Given that many of these vows are made during primary campaigns, when candidates are eager to appeal to a narrow slice of the electorate, often in a single state, you would think that, once elected, presidents would jettison far more of their promises.

Bush’s experience surely serves as a deterrent. But candidates also tend to promise the kind of policies that they actually think are good. In addition, they promise policies that attract strong backing in their political party, which is another argument for watching their policy proposals closely. If you take seriously the idea that political parties are composed of people who try to use the most appealing-seeming candidate as a vehicle for the most extreme agenda they can get away with — and, as I’ve argued previously, you should take that idea seriously — then watching candidates’ policy promises tells us what their party actually wants. Once in office, politicians will try to please their party, if only to forestall a primary challenge.

Ultimately, there is no alternative to taking policy positions seriously. Should we watch a candidate’s political positioning? His ads? His record in a state where the political parties and interest groups are very different than they are on the national level?

The evidence says no. Although presidents mostly follow their policy promises, they typically ignore their political positioning. Obama ran on changing Washington, but he’s worked within the system to achieve his goals. George W. Bush ran as a “uniter not a divider,” but his agenda caused deep divisions, and he decisively chose a side. In the end, politicians position themselves in whatever way advances their goals. And those goals, put simply, are getting elected and passing their policy preferences into law. We don’t yet know who will be elected in 2012. But we do know the policy preferences of the major contenders. As a result, long before he is elected, we will know the agenda of the next president.