CNN contributor and Republican consultant Alex Castellanos waded into birther conspiracies to excuse Mitt Romney's refusal to disclose his tax returns, arguing that Romney should withhold his tax returns until President Obama “releases 10 years of birth certificates.”

Noting the increasing pressure for Mitt Romney to release his tax returns, The Washington Post's Chris Cillizza and Aaron Blake reported:

“Let's say Mitt Romney released 100 years of tax returns tonight,” said Alex Castellanos, a Republican media consultant who advised Romney in 2008.  “What do you think the odds are that the Obama campaign would say, 'Oh great Mitt. Thank you! Now we can put that behind us and move on to more substantive issues like entitlement reform!' Zero.”

Added Castellanos: “I'd advise Mitt to release 10 years of tax returns when Obama releases 10 years of birth certificates.”

Castellanos appeared on CNN as recently as Tuesday.

This is not CNN's first brush with on-air personalities dabbling in birtherism. In 2009, Lou Dobbs spent several months exploring what he said were “new questions” about Obama's birth certificate - a campaign that eventually contributed to CNN's decision to part ways with Dobbs.

Castellanos' nod to the birthers is also at odds with comments he previously made expressing hope that the silly birther thing was finally over.

In April 2011, after Obama released his original birth certificate, Wolf Blitzer asked Castellanos whether that would finally end the birther controversy. Castellanos responded:

You know, we certainly hope so, because there's certainly enough serious issues confronting the United States and questions about President Obama's leadership. I mean, if we're going to release a long form, it would be great to see the longer explanation of how the president wants to spend more in Washington while reducing the deficit, how he's going to stimulate the economy while taking tax money out of it, how he's going to win a war in Libya while he's trying to get out of the war in Libya. There's a lot of other things we could talk about other than something I think the president has put to bed today. 

It's difficult to put the birther issue to bed when people like Alex Castellanos invoke it when it serves their political agenda. 

UPDATE: As Steve Benen noted, Castellanos' comparison of the birther conspiracy to Mitt Romney's undisclosed tax returns serves to whitewash the substantive, unresolved questions surrounding the candidate:

There are a couple of angles to this to keep in mind. The first is that really are legitimate questions that voters deserve answers to, and those answers are only available in the documents Romney is inexplicably keeping secret. No one is characterizing this as some kind of procedural hurdle that must be cleared; it's about resolving lingering, relevant questions about Romney's background.

Indeed, Romney publicly gave his word, on camera, that he would "go back and look" to let us know what tax rates he paid over the last decade, and it now appears the candidate will break that commitment without explanation.