Nate Silver believes so - and has some good evidence to back him up. I know they are tilted right editorially, which is their prerogative, but I didn't realize they were now massaging their polls to favor McCain:

Look -- I'm not going to tell you that my site is completely devoid of spin. I am a Democrat, and I see the world through a Democratic lens. But what I can promise you is that we'll keep the spin separate from our metrics. The spin is a side dish, which you can choose to consume or ignore.



Unfortunately, that is not a choice you have at RCP. Their partisan leaning is infused into their numbers. If RCP disclosed their methodology -- articulated their rationale for excluding or including certain polls -- I would give them the benefit of the doubt. But they do not, so I do not.