Howard Kurtz wonders if Barack Obama has "lost" Jon Stewart's support. I suspect there are two factors at work here. One is that a lot of folks who lean left have gotten frustrated with the president for lack of action. But I think also it's simply becoming more possible to make jokes about the man. It's always difficult with a new face on the scene to find "access points," things about the subject that lead to humor…but eventually they emerge. Quirks become exaggerated. Flaws become more obvious. I seem to remember some prominent political cartoonist — may have been Paul Conrad — saying that the longer an elected official was in office, the easier he or she became to caricature.