Stewart and Colbert have the exact same fanbase
That's not necessarily true.
Stewart's fanbase has always been fairly diverse, with representation from all demographics. But Colbert's is very clearly skewed in favour of the young, not the young at heart. When character Colbert came along, Stewart receded into the background as far as youth audiences are concerned. Young people still watch Stewart, but they're like Big Band Jazz listeners when bebop came along - a minority.
Sure, a lot of leftwing nutjobs called Bush Hitler, but that was never much more than a minority of people on the left.
You should have disabled your browser's content filter and pop-up blocker during the Bush Administration.
…though in all seriousness, people HAVE become a lot more uncouth in public recently. It's appalling such behaviour is being tolerated, but it's true the sensationalist media is helping to paint the idea those kinds of actions are acceptable. Yet, it only seems so omnipresent because of the powerful presence of Democrats in Congress and the White House.
If the Democrats get slayed in the upcoming mid-terms, we'll get see if conservatives get the same treatment the liberals are suffering through now. Otherwise, we'll have to wait until the next conservative president/majority, and who knows if this mania will have died down by then?