The Washington Times or the Evening Standard would be perfectly reasonable sources for evidence. Rush Limbaugh I suspect rather less so.

When it comes to evidence, I often prefer to use versions of news stories from the Daily Telegraph rather than the Guardian, to avoid the assumption that there might be a "liberal" bias. (Though I am aware that in American terms the Daily Telegraph, supporting the UK Conservative Party as it does, might count as a bit left-wing at times in USA politics.)

Opinion pieces are not evidence. People tend to link to them, or post extracts from them, because they think they more clearly represent the point of view of the poster than anything they might write. They are very often wrong in this - first-person comments are often more persuasive.

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I agree with Ebbie there - Obama seemed to deal with that question very well. If McCain or his scriptwriters had not decided to use it, I doubt if it would have been blown up into anything. I've often seen politicians, left and right, floored by unexpected questions, but this wasn't an example of that happening.