The so-far-unaired John McCain ad attacking Mitt Romney – first shown by John Dickerson at Slate – strikes me as extremely effective. Why isn’t McCain, or some other Republican candidate, airing it, or some version of it, now? We’ve all seen the various videos from the past, sometimes the pretty recent past, of Romney being strongly pro-choice, speaking in favor of Massachusetts gun control laws, and distancing himself from Ronald Reagan, and it’s very easy to cut to video of him saying far different things today. Yet until now, with McCain’s “phony” ad, there haven’t been attack ads against Romney – while Romney has aired several against Huckabee and McCain. Both Huckabee and McCain have struck back verbally – yesterday McCain, when asked why he didn’t respond more forcefully to Romney’s attacks on immigration, said, “Never get into a wrestling match with a pig. You both get dirty – and the pig likes it.” But that name-calling, like the “phony” ad, doesn’t seem nearly as effective as an ad starkly contrasting Romney with himself. Certainly Romney’s money – I suspect that in this last quarter of the year, despite his impressive fundraising, he will be nearly, and perhaps actually, a majority self-financed candidate – allows him to swamp his opponents in terms of the sheer number of airings. But a single ad can sometimes have quite an effect. If the situation were reversed, does anyone doubt that Romney would use such material against his opponents?