The mainstream media, to their credit, have latched onto the fact that Mitt Romney won’t describe roughly half of his tax plan—something sure to come up in tonight’s debate. Romney pledges to reduce taxes by $5 trillion through well-detailed cuts, but since Republicans are deeply concerned about the deficit (ahem, cough) Romney claims he would also eliminate or reduce tax breaks to make up for the lost revenue and make the plan deficit-neutral. He just won’t say which ones.

There’s a reason for that—independent analyses show Romney would have to cut popular deductions used by the middle class in order to truly offset the lost revenue. He denies this, of course, but it’s hard to believe Romney if he won’t actually explain the details. (This week his campaign floated a plan to cap deductions at $17,000, which still won’t make the math work).

This rather shocking lack of specificity lead even Fox News’s Chris Wallace to go after Paul Ryan this weekend in a quest for details, an indignity Romney has repeatedly suffered as well. The Obama campaign has relentlessly hammered the Romney/Ryan ticket on this point, and openly told reporters this week that since “Romney won’t name which deductions he’ll eliminate,” Obama will press him to do so during tonight’s debate.

But frequently lost in this conversation is the fact that Romney has, in fact, named three (and only three) specific deductions that he would reduce. Not surprisingly, they mainly affect low-income families. I’ll pull from the Center for American Progress’s lengthy examination of Romney’s economic policies earlier this year for the details:

Eliminate President Obama’s American Opportunity Tax Credit for families paying for college

Under the current American Opportunity Tax Credit, families are eligible for a tax credit of up to $2,500 for four years of college (partially refundable for families with no income tax liability). Under Gov. Romney’s plan, credits would be limited to a nonrefundable credit of about $1,800, available only for two years of college.

Reduce the Earned Income Tax Credit for larger families

The Earned Income Tax Credit supplements the earnings of low-income families, rewarding work while offsetting payroll and other taxes. Prior to 2009, families with three or more children received the same tax benefit from the Earned Income Tax Credit as families with two children, despite a higher cost of living. A provision enacted in 2009 made such families eligible for an additional benefit, but Gov. Romney’s plan would let that provision, along with another improvement to the credit signed in 2009, expire. A two-parent family raising three children on $30,000 of earnings would lose $1,076 a year.

Lower the Child Tax Credit for low-income families

The Child Tax Credit also rewards work while defraying child rearing expenses. Only families with earned income can benefit. The credit is generally $1,000 per child, but families at low-income levels can often claim only a partial credit. President Obama’s 2009 reforms allowed low-income families to claim more of the credit. Gov. Romney’s tax plan would repeal those reforms, resulting in a smaller credit or no credit for the families of 15.8 million children.

All told, CAP calculates that by letting these three reforms expire—which, again, Romney has explicitly asserted he will do—18 million households would see higher taxes, including 13 million families with children. (Which, by the way, is 27 percent of all families with children). These are all tax provisions Obama has pledged to extend.

So if Romney says tonight that he won’t raise taxes on the middle class (as he said at the RNC) that is not true—it can be debunked without even getting to the hairy debate about unnamed exemptions and deduction caps. And if Romney gets hammered for refusing to name what deductions he would reduce, that is not really true either—he’s named these three, which would hurt exclusively low- and middle-income families.

That’s perhaps a good a hint as any about what other deductions President Romney would end up targeting.

For more on Romney’s seeming inability to talk about specifics in his plan, watch Katrina vanden Heuvel’s appearance on Now With Alex Wagner.