[Updated: See below.]
Mitt Romney has made public his federal income return for tax year 2010 together with an estimated return for 2011. His campaign indicates that other than the final version of the 2011 return, no more will be forthcoming. The question is why.
In recent decades, almost all presidential candidates have released more than two years of returns. As far as I know the only other candidate to limit release to just two years was John McCain in 2008, but there were no serious questions about Senator McCain's finances. When Mitt's father George ran for president in 1968, he released a dozen years' worth of returns. George Rommney said, if I recall correctly, that voters should be able to see more than a year or two of them in order to see how a candidate has conducted his financial affairs over an extended period of time, not just while running for president.
Incidentally, yesterday one of Romney's senior advisors, Ed Gillespie, erroneously said that John Kerry released only two years' worth of tax returns when he ran for president in 2004. In fact, as National Review has pointed out, Kerry released five years of returns when running for president and had already released the previous 15 returns during his Senate campaigns. To match Kerry's 2004 precedent, Romney would need to produce the last 20 years of tax returns. [A previous version of this post said that Kerry released two years' returns in 2004 and 18 previously; I erroneously supposed that Gillespie had been at least partly correct. Mea culpa.]
Romney's opponents have suggested that seeing returns from earlier years would help answer questions about his holdings in Switzerland, the Cayman Islands, and other notorious tax havens. A number of fellow Republicans have urged Romney to release more returns, including former Republican National Committee head Michael Steele, conservative strategists and commentators John Weaver, Ana Navarro, Bill Kristol, and George Will, political consultant Matt Dowd (chief strategist for the Bush-Cheney 2004 presidential campaign), Alabama Governor Robert Bentley, former Mississippi Governor Haley Barbour, and others.
To be clear, at this point there's no indication that Romney did anything illegal or even necessarily questionable (though the accounts in offshore tax havens are at least a bit fishy). So it's puzzling why Romney would not just make the problem go away by releasing his returns going back at least six or eight years and better yet twelve (like his father) or twenty (like Senator Kerry). Yesterday on ABC News, George Will said, "The costs of not releasing the returns are clear, therefore he must have calculated there are higher costs to releasing them." Other politicians and commentators on the left and right have suggested the same, and for what it's worth that sounds pretty likely to me as well.