Mitt Romney has released his 2010 tax return and says he “might” release his 2011 return when it is complete (he filed an extension until Oct. 15). He has refused to provide additional tax returns. The more he resists, the more we wonder what he might be hiding. I have some ideas.

His 2010 return showed a 14.9 percent overall tax rate, largely because he was able to take advantage of the carried interest provision in the tax code, a loophole that allows him to pay capital gains rates on income generated without having any personal capital at risk. While legal, it is a sham, and he may also have had years where he paid even less. The tax returns may also show significant income from Bain Capital when he was off “saving the Olympics” and supposedly no longer an active member of the management team. Speaking of management, Mr. Romney heralds his experience as CEO of Bain Capital, a company that had a grand total of 115 employees when he “left” in 1999.

Conservatives, led by Fox News, bellowed about President Barack Obama’s birth certificate for years, insisting on seeing the “long form” of that document. He consented. Now it’s time for Mr. Romney to show 10 years of tax returns.