Sometimes, in the midst of all the campaign blather and spin, saying nothing at all is the most effective way to communicate. That’s the rationale behind Rick Santorum’s latest ad blasting Mitt Romney. For months Santorum has tried to focus attention on the liberal components of Romney’s past, confronting him in debates and on the stump. But now, less than a week before the high-stakes Michigan primary, Santorum’s campaign has decided to let Romney hang on his own words.

The ad, set to air this weekend in the Wolverine State, compiles Romney’s past quotes about gun control, congressional earmarks, abortion, and health-care reform. All, the spot implicitly alleges, contradict Romney’s current positions on the same issues.

The former Massachusetts governor’s 2002 quote, “I will preserve and protect a woman’s right to choose,” appears in white print against a black backdrop and seems to be the exact opposite of Romney’s more current pronouncement, as recently as Tuesday: “I’m pro-life. I’m in favor of protecting the sanctity of life. I will cut off funding to Planned Parenthood.”

Other unfortunate contradictions follow, including “I’d be embarrassed if I didn’t ask for federal dollars every chance I had,” another quote from Romney’s 2002 gubernatorial campaign in Massachusetts that now has become a shameful statement to the growing base of fiscal conservatives. And then there’s an old quote from The Boston Globe: “I don’t line up with the National Rifle Association,” he once said, a head-scratching affront to Romney’s now sweepingly pro–Second Amendment position. Romney’s presidential campaign reflexively called the ad “dishonest” in an attack on Santorum, but wouldn’t elaborate about what was inaccurate about its message.

It’s true that Santorum cherry-picked the most stunning quotes and positions from Romney’s past. Some, it appears, are even slightly out of context, like the federal-money quote, which Romney said while running for office to emphasize that as long as the federal government was giving out money, he wanted to make sure it wasn’t being spent only in other states. Santorum also pins a $700 million increase in taxes and fees in Massachusetts on Romney, which is only part of the story—many state tax rates went down during Romney’s tenure, but overall revenue increased.

Yet the effectiveness of the spot is that there really isn’t room for spin. Rather than start a debate, as most ads do, this one simply puts the onus on the former governor to twist himself into a pretzel to explain why his current positions contradict old ones from his time as governor.

Democrats have grasped the same theme, attacking Romney as a flip-flopper and political opportunist willing to say whatever sounds good to the voters he’s attempting to court. Using the Republican frontrunner’s words alone, it’s an argument he’s found hard to compellingly refute.