But more worrying for CCHQ than short-term poll slides is the potential for this to recontaminate the brand, especially by injecting some kind of "Tory toff" poison into the political bloodstream. Sure, the charge hasn't stuck when Labour have deployed it. And given the cross-party nature of the expenses scandal, I doubt they can deploy it in future. But that doesn't mean that "Tory toffs" can't germinate and spread as an idea all by itself. If anything's going to encourage it, then it's papers stuffed with the phrase "Tory grandees," alongside mentions of tennis courts, hedges and helipads.
Don't get me wrong. I think the vast majority of British voters aren't given to class politics. But this goes beyond class: a spilt between decent folk and venal politicians; between workers and parasites; between, in the end, good and bad. I've said it before, but it bears repeating: Cameron's got to act.
To be fair to the Tory leader, he's struck the right tone in media appearances this morning, saying that the claims are "out of order," and that he is going to "deal with it". But what does that mean in practice? The open publication of all Tory receipts? Resignations and suspensions? Or (an interesting idea mooted by CoffeeHouser Nick, among others, earlier) an expenses amnesty? Whatever, it shouldn't just be about capitalising on the situation - although Cameron can certainly do that at Brown's expense - but, rather, restoring the public's faith in our Parliamentary democracy.