Daryl Cagle keeps an extremely useful collection of major editorial cartoonists' efforts on various issues of the day at his high-traffic site. If you have a moment, I think it's worth looking at the section on 9/11's five-year anniversary. It's really only when you see a cross-section of cartoons on an issue that massive and historically important that one begins to grasp what may be pushing American newspaper editorial cartooning into the margins of public discourse.
It's not the visual sophistication of the cartoons or even the cartoonists' ability as a group to grab an issue by the shoulders and head-butt it in the chin that one calls into question; it's more like our appetite for imagery has been satiated and the role of the strong, single statment has been subverted long before we open the newspaper to page three. It makes sense that our best editorial cartoonists have the authority of clear-eyed, raised-voice anger (Oliphant) or the mental agility that allows for a perspective so fresh it causes people to lean in and listen (Toles); it's not a matter of assuming the stage anymore, it's more like working a cocktail party where everyone is five-eighths drunk.
