What are wedge issues? Well, a lot depends on whom you ask. Political consultants usually define them as issues that unite the base but split the opposition. The most familiar examples are guns, God and gays. But they can include everything from the Pledge of Allegiance to crime.
Traditionally, conservatives are cast as the villains in the wedge-issue story. And there's some truth to the tale. What initially offended liberals was the way Republicans made race and civil rights issues for national discussion (ironic considering how liberals are always clamoring for a "national conversation" on race). Liberals will tell you that Republicans shattered the consensus on civil rights by running on racially charged issues. Conservatives will say that liberals invited a so-called "racial backlash" by going too far on issues like quotas and being soft on crime.
I think conservatives have the better argument in that fight, but that doesn't mean Republican politicians were angels in every contest.
Regardless, it didn't take long for Democrats to expand the definition of wedge issues to include pretty much any issue they didn't want to talk about.
In his book "What's the Matter with Kansas?" Thomas Frank insisted that Republicans only know how to win on divisive wedge issues that distract voters from their "real" interests. This amounted to McMarxism -- a dumbed-down, mass-market version of the old socialist notion of "false consciousness." Liberals like Frank assume voters are too dumb to know what they should care about.
President Obama subscribes to a similar view of the world, as when he explained that Democratic (!) voters in western Pennsylvania weren't supporting him because they were too "bitter" and determined to "cling" to their petty bigotries and cultural prejudices.
Looked at from a broad historical perspective, complaints about wedge issues are really gripes about declining liberal power. Democrats take it as a given that the old New Deal-Great Society coalition is the natural order of things, and that members of that coalition -- everyone from minorities and intellectuals to working-class whites and union members -- belong in their column no matter what. Any effort to peel off any of those constituencies is therefore unfair or illegitimate.
This is ridiculous, of course. First of all, democracy itself is about disagreement, not agreement. Politics is about having arguments about what our priorities should be. It is inevitable that there will be winners and losers in those arguments.