That Mitt Romney will lie about anything - no matter how major or mundane - is virtually taken for granted by the press and the public alike. Steve Benen has created a cottage industry cataloguing Romney's lies, an encyclopedic task now up to Volume XI. As Jonathan Chait explained, there's even a clinical term for Romney's pathological aversion to the truth (it's called "fundamental attribution error"). And when the 2012 GOP frontrunner isn't misrepresenting his positions on the issues, he's comically reversing them altogether. It's no wonder even conservative columnist George Will mocked Mitt as "recidivist reviser of his principles" who lacks "the courage of his absence of convictions."
But while Mitt Romney is even deceitful about his sins of commission (declaring "I think you'll find that I've been as consistent as human beings can be" after having declared "if you're looking for someone who's never changed any positions on any policies, then I'm not your guy"), in rare moments of candor he is honest about his sins of omission. That is, in his perpetual quest to avoid alienating voters certain to dislike his policies, Romney admits he keeps the details to himself.
For months, the Romney campaign auto-response of "no comment" has been on display across a gamut of issues ranging from the mass deportation of illegal aliens and Ohio's anti-labor laws to extension of the payroll tax cut and even GOP debate attendees booing a gay active duty U.S. soldier. But in a December interview with the Wall Street Journal, the RomneyBot admitted his cowardice is a feature and not a bug:

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."

Unfortunately, what Mitt Romney branded "demagogues" most Americans call "voters."
Even when he rolled out his new 20 percent across-the-board tax cut as a bribe for those supposed demagogue-voters, Governor Romney refused to say how he would keep his pledge to "Cut, Cap and Balance" the budget. Even by taking an axe to domestic spending, his proposal to both massively cut taxes for the wealthiest Americans while increasing the defense budget would produce a much larger 10-year debt than President Obama's FY 2013 plan. Unless, that is, Romney is willing to eliminate deductions for workers, families and businesses that cost Uncle Sam over $1 trillion a year. But in typical Romney fashion, his campaign is refusing to say which loopholes it would close while promising to maintain the ones voters care about most. 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." For his part, Romney promised only "I want to make sure that you understand, for middle-income families, the deductibility of home mortgage interest and charitable contributions, those things will continue."
But asked to get specific about his self-proclaimed "bold" tax plan, Mitt Romney decided discretion is the better part of valor. As he explained earlier this month, Romney in essence responded, "I'm not going to tell you":

"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."

As Ezra Klein's Wonkblog rightly concluded:

"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."

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."

But as Rick Perlstein suggested in Rolling Stone, the roots of Romney's horror at telling voters anything they may not want to hear dates back further. Apparently, Mitt concluded that his father George Romney lost his bid for the White House in 1968 by leveling with the American people. George's "shocking authenticity," Perlstein argued, cost him the GOP nomination. And that's a mistake his son Willard has no intention of making:

The truth was a dull weapon to take into a knife fight with Richard Nixon - who kicked Romney's ass with 79 percent of the vote. When people call his son the "Rombot," think about that: Mitt learned at an impressionable age that in politics, authenticity kills. Heeding the lesson of his father's fall, he became a virtual parody of an inauthentic politician. In 1994 he ran for senate to Ted Kennedy's left on gay rights; as governor, of course, he installed the dreaded individual mandate into Massachusetts' healthcare system. Then he raced to the right to run for president.

The result, conservative columnist Ross Douthat fretted in December 2010, is that Romney is "serially insincere." Nevertheless, Douthat warned his readers that trait was a plus for Mitt's supporters:

Nearly every position he stakes out comes across as a blatant (and often inconsistent-looking) pander to a conservative electorate that regards him with suspicion. But there are good ideas concealed within the pandering -- you just have to know where to look! And in your heart, you know he's a smart guy who'd make a solid center-right president -- wonkish, detail-oriented, sensible on policy, all the rest of it. He's just a prisoner of the process!...Even when he's mid-pander, you always know that he knows that it's all just a freak show, and you can always sense that he'd rather be at a policy seminar somewhere, instead of just forking red meat. There's a highly competent chief executive trapped inside his campaign persona, in other words, and the only way to liberate him is to put him in the White House!

While Romney's backers may view his duplicity as a virtue, even Douthat is unconvinced. "Because everything he does feels like a pander," he worried, "I don't know where he really stands on any of them."
Which is probably just how Mitt Romney wants it. (While his closest adviser Eric Fehrnstrom compared Mitt to an "Etch-a-Sketch," in 2005 his strategist Michael Murphy admitted his man was "a pro-life Mormon faking it as a pro-choice friendly." ) After all, when he's not pandering to voters, he's keeping silent altogether on what would actually do in the Oval Office. As he put it in response to the growing outcry for the release of his tax returns:

"I don't put out which tooth paste I use either. It's not that I have something to hide."

Instead, Mitt Romney would have you believe, "you can't handle the truth." Or to put it another way, Mitt Romney can't tell the American people what he would do in Afghanistan, how he would balance the budget, what tax loopholes he would keep or kill, or just about anything else.
After all, he's running for office, for Pete's sake.