The “Today Show” on NBC this morning had a long segment on the increasingly partisan nature of American political debates. It featured a couple of professors claiming that America’s two main political parties are increasingly ideological, the Republicans becoming more exclusively “conservative” and the Democrats more exclusively “liberal.” This was proffered as an explanation for the allegedly growing polarization of political discussions in America today.

This is becoming received wisdom. (Here is an article about it from the Cleveland Plain Dealer, but there are lots more out there.) But as Laurence M. Vance pointed out, the latest “Conservative Index” published by The New American presents evidence questioning the received wisdom.

The Index rates congressmen on the basis of “their adherence to constitutional principles of limited government, to fiscal responsibility, to national sovereignty, and to a traditional foreign policy of avoiding foreign entanglements.” The Index gives each member of the House and the Senate a score between 1 and 100, with 100 representing perfect allegiance to those principles as reflected in their record in several recent votes. One person in the House got a perfect score: Ron Paul (R–TX); the highest-rated person in the Senate was John Ensign (R–NV) with 80.

But here’s the interesting part: the average in the House is 46 and the average in the Senate is 41. Thus with all those allegedly ideologically conservative Republicans, both houses don’t even make it halfway to “conservative.” Tom Delay, the House Majority Leader, scores 41, and Bill Frist, the Senate Majority Leader, scores 43. Their respective Democrat counterparts, Nancy Pelosi and Tom Daschle, scored 27 and 30. So the Republican leaders are more “conservative” than the Democrat leaders. But don’t get too excited: that arch-Liberal Ted Kennedy scores 38, only whisker below Delay and Frist.

Vance takes the result to indicate that Republicans aren’t really “conservative” at all, despite what they say and what is commonly said about them. That seems a valid inference, but what strikes me is the credence it lends to the common libertarian complaint that there is no difference of substance between America’s two major parties. And it seems to undermine the idea that the parties are so far apart.