Weird. Rush has spent the better part of the past 6 years identifying the failure of the RNC and the consultants, and was pretty clear neither McCain nor Romney were good choices. He carefully danced around the issue last year because he knew anything he said would be magnified by the media to divide the GOP voters...but it was clear. With McCain, not so much. He has no love lost.
There's absolutely no need for Rush to dance around the issue of McCain being an absolute failure because I'm sure 99.999% of Rush's audience feels the same way about McCain.
Rush is one of these radio guys that knows his audience.