New York‘s Jon Chait thinks that of all the devil’s bargains Mitt Romney had to negotiate in order to secure the presidential nomination of a party that doesn’t trust his conservatism, the “pander to supply-siders” reflected in his tax proposals could turn out to be the most damaging. Why? Because Mitt’s efforts to disguise the regressive distributional effect of his proposals pretty blatantly violate simple rules of arithmetic.

Team Romney, of course, is trying to dismiss the arithmetic lessons being handed out this week by the Tax Policy Center and the Obama campaign as “partisan,” deploying the ancient political trick of challenging the credibility of critics rather than the facts and logic they offer. But that’s where they may be fatally miscalculating, not just on Romney’s tax proposals but on the even broader front of the Ryan Budget that encompasses the heart of the GOP agenda. Maybe Team Mitt can throw sand in the eyes of MSM observers and swing voters with their efforts to obscure the details and ultimate impact of their proposals. But the problem is that the conservative activists who extracted all these policy commitments from Romney in the first place don’t want him to get away with lying, because they agree with the criticisms and are proud to embrace the values and priorities Romney’s being attacked over.

Is Romney’s tax plan regressive? Damn straight it is, conservatives think, and that’s a good thing since the current tax code’s progressivity is an immoral assault on the success of job-creators! Is the Ryan Budget just a modest effort to “reform” entitlements and restore sanity in federal spending, as the Romney campaign’s occasional references to it suggest, or instead, as critics claim, the first step in a crusade aimed at shredding the New Deal and Great Society safety net? Most red-blooded conservatives are strongly committed to the latter proposition, and they want Mitt to own up to it as well, because they quite frankly don’t trust him to stick to the spirit and letter of their agenda.

This central contradiction in Romney’s campaign explains better than anything else why every discussion of his policy platform is perilous for Mitt, and why his failed efforts to campaign on his biography are a big, big problem. Yes, he can continue to lie about his proposals and try to change the subject via attacks on Obama. But sooner or later, his own party base will demand the truth, if only to ensure that he will stay with the program once he is elected. And then the fundamental mendacity of his campaign will no longer be a partisan claim, but a stipulated fact.

Ed Kilgore

Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.