One objection I’ve encountered to my column arguing that the growing DeMint caucus in the Senate is a good thing: if Republicans have fewer than 60 votes (a virtual certainty) a group of particularly uncompromising conservatives could make the perfect the enemy of the good and empower John McCain to cut deals with liberal Democrats.

My first reaction is that Rand Paul, Mike Lee, and Ted Cruz were not nominated in a vacuum. They defeated Republicans who were too willing to compromise with Democrats and who were not sufficiently strict constitutionalists. And in many cases, the establishment Republicans they beat in their primaries would have been considered conservative enough as recently as when George W. Bush was president. So where is the center of gravity in the party?

If you are Lindsey Graham and you face a possible primary challenge in South Carolina in 2014, would you rather side with Jim DeMint and Rand Paul? Or would you rather vote with your buddy John McCain and some liberal Democrats? Graham’s preferences may be the latter, but his political interests are strongly aligned with the former. If you are President Romney, is it in your interest to have a McCain-Kerry policy agenda or one that is broadly supported by the conservatives in your party? Again, Romney’s preferences may be less important than his political incentives.

One area where a bipartisan moderates and McCain coalition could carry the day is on the federal budget. (This scenario assumes a President Romney.) The House-passed budget will almost certainly be a version of Paul Ryan’s plan, perhaps nudged slightly to the left for Romney’s benefit. This year five mostly moderate Republicans voted against Ryan, but many conservatives expressed concern that his plan didn’t cut spending or balance the budget fast enough.

But McCain voted for the Ryan budget. Rand Paul was the only the only senator who voted against it on purely conservative grounds. Whatever their concerns, DeMint and Lee voted for it. So did Pat Toomey. And remember the 2012 debate happened when there was no chance a Democratic Senate and president would ever have allowed the Ryan budget to become law. Next year, if Romney is president, the debate will be less theoretical.

Even here, having conservatives who won’t simply vote for whatever budget is cobbled together by Romney and the Republican leadership is helpful. The only way to get the most conservative deal possible is to have at least some conservatives be a realistic no vote if the GOP wants to spend too much. There is a risk of allowing the perfect to be the enemy of the good, but let’s face it: the recent party’s recent track record on spending when Republicans hold power hasn’t been close to good.