Imagine that you are completing your federal tax return. After looking up the tax rate for your income level, you decide you will pay 20 percent less to Uncle Sam. But along with your underpayment, you include a handwritten note to the IRS letting the government know that you promise to make up the difference at some future date by not claiming some deductions to which you are currently entitled. That, you tell the tax collector, makes your tax return "revenue neutral."

If you're like most Americans, your fraud will earn you a fine at best and prison time at worst. But if you're Mitt Romney, you believe that plan qualifies you to be President of the United States.

To understand how Romney's shell game works, a short primer is in order first. In essence, the GOP presidential nominee has proposed what might be called the "Bush-Dole" plan. Under a President Romney, that would make the budget-busting Bush tax cuts permanent, and then enact another 20 percent across-the-board reduction reminiscent of Bob Dole's failed 1996 scheme. As Matthew O'Brien summed it up in The Atlantic:

First, he extends all of the Bush tax cuts. Second, he cuts income tax rates an additional 20 percent. Third, he undoes the tax hikes and credits from Obamacare and the stimulus. Finally, he eliminates the capital gains tax for all but the richest households. The first three parts of this plan shower high-earners with most of the money. The last part is a bit of a fig leaf for the rest of us. After all, the top 0.1% of households earn half of all capital gains. Exempting middle-class households from this tax certainly helps them, but there's just not that much money there.

(It's also worth noting that Romney wants to eliminate the inheritance income tax, a move which could theoretically divert over $80 million from the United State Treasury to his heirs.)

Unfortunately for a man who loves numbers, Mitt Romney's math simply doesn't work.

Not only does his safety-net shredding budget provide yet another massive tax cut windfall for the wealthy, the Romney plan produces red ink as far as the eye can see. The Tax Policy Center estimated Romney's tax cuts would cost Uncle Sam $460 billion in 2015 alone. (Combined with the extension of the Bush tax cuts, the total figure would reach $900 billion.) As ThinkProgress and the Washington Post's Lori Montgomery and Ezra Klein documented, Mitt Romney's risky new scheme makes George W. Bush look like Karl Marx:

Romney's claim that his plan would promote job and economic growth while reducing the deficit is also likely false. The Bush tax cuts were promoted under the same guise, only to blow a $2.5-trillion hole in the federal budget that was accompanied by worst performance of any post-war expansion" for growth in investment, GDP, and job creation. Romney's tax cuts are even more expensive, clocking in at a cost of more than $10.7 trillion over the next decade and reducing revenue to a paltry 15 percent of GDP, according to Linden. Balancing the budget on those terms, as Romney claims he will do, would be next to impossible.

Impossible, that is, unless Mitt Romney eliminates some of the deductions for workers, families and businesses that cost Uncle Sam over $1 trillion a year. And so far, the cowardly Republican nominee has refused to say which ones he would cut.

Earlier this year, his economic adviser, Glenn Hubbard, admitted Romney's cowardice, explaining "it is not his intention to take on any specific deduction or exclusion and eliminate it." Just two weeks later, Mitt Romney refused to reveal which deductions and tax breaks he would end:

"So I haven't laid out all of the details about how we're going to deal with each deduction, so I think it's kind of interesting for the groups to try and score it, because frankly it can't be scored, because those kinds of details will have to be worked out with Congress, and we have a wide array of options."

In response, the Post's Klein could only shake his head:

"Let's be clear on this: A tax plan that can't be scored because it doesn't include sufficient details is not a plan. It's a gesture towards a plan, or a statement of intended direction, or perhaps an unusually wonky daydream. But it's not a plan."

Or at least, not a plan Mitt Romney will speak about publicly. As the Wall Street Journal reported in April:

Mr. Romney discussed his plans while speaking to high-dollar donors at a private estate. During the backyard event, which could be heard by reporters outside on a public sidewalk, Mr. Romney offered policy specifics he has yet to unveil on the campaign trail...

"I'm going to probably eliminate for high-income people the second-home mortgage deduction," Mr. Romney told supporters at the event Sunday. His plans could allow him to keep the same level of tax revenue but to lower rates, which he said would allow small businesses to keep a larger share of their earnings and expand their payrolls.

Sadly for Romney, that small step is nowhere near enough to make the budget math work.

It's important to understand that much of the estimated $1.3 trillion in annual tax expenditures in 2015 (a figure larger than the entire 2012 budget deficit and equivalent to about a third of the $3.8 trillion in federal spending next year) benefit working and middle income Americans. As The New York Times recently revealed, that trillion dollars in annual tax expenditures is now larger than Uncle Sam's take from the income tax each year. And as the Washington Post highlighted last year, "ever-increasing tax breaks for U.S. families eclipse benefits for special interests." For example, the home mortgage tax deduction for all Americans was worth $89 billion in 2011. Tax-deferred 401K accounts cost the Treasury $63 billion. The Earned Income Tax Credit had a similar $63 billion price tag last year.

But Mitt Romney still won't tell the American people which of these tough choices he would make. And as he has repeatedly made clear, that dishonesty and secrecy is a feature, not bug, of Romney 2012.

Romney's penchant for withholding vital information from voters is no accident. As the former Massachusetts Governor inadvertently revealed in an interview with the Weekly Standard, his opacity is by design, a lesson learned from losing the 1994 Senate race:

"One of the things I found in a short campaign against Ted Kennedy was that when I said, for instance, that I wanted to eliminate the Department of Education, that was used to suggest I don't care about education," Romney recalled. "So I think it's important for me to point out that I anticipate that there will be departments and agencies that will either be eliminated or combined with other agencies. So for instance, I anticipate that housing vouchers will be turned over to the states rather than be administered at the federal level, and so at this point I think of the programs to be eliminated or to be returned to the states, and we'll see what consolidation opportunities exist as a result of those program eliminations. So will there be some that get eliminated or combined? The answer is yes, but I'm not going to give you a list right now."

In a December profile by the Wall Street Journal, Governor Romney acknowledged that when it comes to facing the voters, discretion is the better part of valor:

Amid such generalities, it's hard not to conclude that the candidate is trying to avoid offering any details that might become a political target. And he all but admits as much. "I happen to also recognize," he says, "that if you go out with a tax proposal which conforms to your philosophy but it hasn't been thoroughly analyzed, vetted, put through models and calculated in detail, that you're gonna get hit by the demagogues in the general election."

But what Mitt Romney calls "demagogues," most Americans would call "voters." And if they handled their own taxes the way he is proposing to, they would end up not in the White House, but in jail.

(This piece also appears at Perrspectives.)