Glenn Beck lost all credibility with even the GOP and Fox stalwarts long ago. I'm not sure what it was exactly that finally convinced people who didn't already believe it that he was a total nutjob. Maybe it was the whole Obama is a racist who hates white people led to advertisers pulling out, but the show limped on for a while after that. And by limp, I mean only about 20 times more viewers than Rachel Maddow. Although the smart money ran for the hills when they heard him say that shit about Obama being racist, I bet it still went down like a round of free beers among the hardcore Tea Party / Fox News screen lickers.
I read somewhere that by the end, the only thing keeping the Glenn Beck show on air was Jon Stewart's audience, who tuned in for the comedy. They just got bored of the joke. I could personally do with another stint of the Glenn Beck show, as another outlet for criticising Mitt Romney, albeit in totally unfounded accusations of him being a socialist who will turf Americans out of their homes and hand the keys over to illegal immigrants.