Watching Capitol Hill’s leaders stare each other down over the issue of earmarks may seem like watching a game of chicken.

Aren’t Speaker Nancy Pelosi (D-Calif.), House Minority Leader John Boehner (R-Ohio), Senate Majority Leader Harry Reid (D-Nev.) and Senate Minority Leader Mitch McConnell (R-Ky.) all on board the same congressional vehicle? Don’t public opinion polls suggest the vehicle is heading for a ditch? Why don’t leaders on both sides of the aisle grab the wheel together and avert an unpleasant bump?

 There are a handful of reasons. First, each lawmaker frets that abjuring his or her own helping of pork without a guarantee that the other side will keep to a similar regimen amounts to unilateral disarmament. Each earmark is designed to win the votes of people in a given district using money taken from taxpayers everywhere. Thus, each earmark is a net gain for the district and its inhabitants at the expense of all other Americans.

And although most of us are against this sort of thing in theory, few are as unhappy about the project in our own back yards as we are about a boondoggle in some distant corner of the nation. It is a version of the tragedy of the commons; there is no clear owner of the cost of each earmark, so earmarks are overused and the resource — federal revenue — is unwisely depleted.

As Pelosi said of Republicans this week, “They want to beat a loud drum, but when it comes down to it, they want their earmarks.”

Rep. Rahm Emanuel (Ill.), the House Democratic Caucus chairman, claimed credit for his party for reducing earmarking last year. But if he and the party see this reform as a good thing and at the same time acknowledge, as they must, that this Congress is as unpopular as any before it, why isn’t the party running Capitol Hill doing more to rein in the practice that its rhetoric suggests is a bad thing? For example, why not ban “air-dropped” earmarks?

The answer is that the earmarking explosion is more damaging to Republicans, for it has detached them more clearly from the fiscal principles they traditionally trumpet. Thus it is Boehner and the GOP who have most to gain from steep cuts in pork portions. Which is why it is Boehner who is urging bipartisan action and Pelosi who is pointing wryly to Republican ambiguity.

Given that the issue cuts deeper into Republican than into Democratic credibility, it is the GOP that has more incentive to change. Republicans cannot expect Democrats to help them resolve their quandary.