I mentioned to a friend that I was planning to attend this Saturday's march in Washington, D.C., and she replied, "Oh, the Jon Stewart march?" I said, "No, the march planned months ago by real activists." She hadn't heard of it.

Lost in the kvetching and hand-wringing about Stephen Colbert's appearance before a House subcommittee on immigration on Capitol Hill has been a serious discussion of the limits of comedic politics. Without question, Colbert (in the role of the hilariously self-absorbed, irrational conservative host of a late-night show) and Jon Stewart, whose Daily Show regularly provides better political analysis than evening news shows and Sunday-morning political talk shows, should be commended for their often brilliant and courageous engagement with the excesses of right-wing political talking points.

Their work came to popularity precisely because the mainstream media had largely abandoned their obligation during the Bush years to question and to push hard against the propaganda offered by an administration that showed contempt for transparency. Colbert's performance at the 2006 White House Correspondent's Dinner, when he faced down President Bush and the entire co-opted White House press corps with a searing indictment of the press and administration collusion, stands as one of the most fearless and brilliant comedic performances of the last 50 years. The silence in the room was made up of both astonishment and shame, and the evening may have represented a turning point in the mainstream media's slow attempt to redeem itself from its embarrassing abdication of rigor during the Bush years.

Stewart and Colbert have formed a kind of "keepin' it real" tag team, exploring the hypocrisies of politics and politicians, and demanding that we confront the absurdities of absolutist, right-wing bromides. The video footage Stewart uses to critique political posturing is as much an indictment of real television news shows that refuse to do the kind of background work Stewart's team manages to do nightly as it is a brilliant sendup of the increasing irrelevance of truth in American politics. That Stewart and Colbert are so consistently funny is a testament not only to their talent but also to the discipline and hard work they bring to each night's performance.

But Colbert and Stewart are not real political activists. Some would say that this is what makes them so effective. Without a doubt, they have introduced a whole generation to critical political thinking. But Colbert and Stewart are comedic performers who host television shows. They may decide that they prefer acting in movies or doing stand-up or writing humor books (as they have both done). Their television shows may be canceled if they fail to garner sufficient ratings.

They cannot (nor do they purport to) offer any sustained opportunity for political transformation in this country. It's also worth pointing out that their audience is a narrow one: young, college-educated, middle- and upper-middle class -- and white. And -- judging by the intensity of the male banter on their shows -- disproportionately male (count the number of times Stewart uses the term "douche bag" in a week).