In last night's debate, Mitt Romney was asked by both debate moderators and his fellow candidates whether he would release his tax returns. This being Romney, we didn't get a straight answer—in fact, the number of Twitter users who thought Romney was dodging his answer was so off the charts that Fox News couldn't record it.

Today, Romney actually admitted that he pays a different tax rate than the average American, telling reporters in South Carolina, "What’s the effective rate I’ve been paying? It’s probably closer to the 15% rate than anything. My last 10 years, I’ve—my income comes overwhelmingly from some investments made in the past.”

So why is Romney defying tradition—a refusal the New York Times calls "impossible to defend"? What does he not want voters to know?

For one, Romney made millions of dollars laying off workers and bankrupting companies as the head of Bain Capital. The income from his Bain investments is taxed at a far lower rate than the wages of middle-class workers like teachers and police officers. Warren Buffett, for example, famously pays a lower tax rate than his secretary does. But Buffett wants to level this unfair system. Romney does not.

As the Washington Monthly's Steve Benen notes, "The politics of this are awful for the likely GOP nominee. Working families probably won’t be amused to learn Romney—the guy who got rich laying people off, and has been a professional candidate for the last six years—pays a lower tax rate than they do. They’ll be even less pleased to know Romney, if elected president, will fight to keep it this way, even when he calls for tax increases on those struggling most."

In 2008, President Obama released eight years' worth of tax returns well before he received the Democratic nomination. In fact, decades of presidential candidates, including Romney's father, have made it standard practice. Romney himself once saw the value in transparency: In 1994, when Romney was running for Senate against Ted Kennedy, Romney called on Kennedy to release his own tax returns. (Of course, Romney didn't even release his own that year.)

Romney needs to release his tax returns now—and more than just a year's worth. It's high time Romney played by the same set of rules as every other presidential candidate.