The old saw, “If you don’t have anything nice to say, don’t say anything at all” works as motherly advice or as a pithy rule of thumb to aid character formation. But it fails spectacularly as a guiding political strategy for a presidential campaign.

As Aaron Tippin sings in that most red, white and blue musical genre — country — “You’ve got to stand for something or you’ll fall for anything. You’ve got to be your own man, not a puppet on a string.”

According to a recent Wall Street Journal/NBC News poll, “Nearly three in 10 voters, 29 percent, pointed to McCain as the candidate running a negative campaign, compared to just 5 percent who said Obama is running a negative campaign.”

Prevailing wisdom would label this perception a minus for Big Mac. But it shouldn’t. Consider this example from the recent past:

During the Republican presidential primary season earlier this year, former Massachusetts Gov. Mitt Romney weathered heavy criticism for daring to run ads that harshly contrasted his attributes with the perceived failings of a major opponent, Mike Huckabee. His first such ad, which ran in Iowa in December, described Romney and Huckabee as “two good family men,” both pro-life and both in favor of keeping marriage between a man and a woman.

But the similarities ended there. The ad continued: “Mitt Romney stood up and vetoed in-state tuition for illegal aliens, opposed driver’s licenses for illegals. Mike Huckabee? Supported in-state tuition benefits for illegal immigrants. Huckabee even supported taxpayer-funded scholarships for illegal aliens.”

What, pray tell, is wrong with an ad like that? It makes its point decently, by taking a hard look at the respective records — exactly how a candidate should clarify the differences between himself and an opponent.

Despite some initial dithering about scruples, Huckabee eventually fired back, running an ad that accused Romney of “dishonesty.” Among other things, the ad aimed to present Romney as something other than a law-and-order executive.

As the Annenberg Political Factcheck Web site pointed out, though, that portrayal was a bit misleading: “The ad says Romney’s record as governor of Massachusetts includes ‘no executions.’ That’s true, but the reason is that Massachusetts doesn’t have a death penalty. Furthermore, Romney tried and failed to get the death penalty reinstated.”

The fact of the matter is that Huckabee, in spite of his professed dislike of negative advertising, wanted to win, and knew the power that such ads command — although in this case, they stretched the truth. The pastor in him wanted to say (or thought he should say), “Negative is bad.” But in his political heart, he knew what was right for his cause.

But it’s more than that: Politics cannot always center on the quest for popular celebrity. Barack Obama is reminded of this whenever he’s made to talk about real political issues. John McCain should make him do it more often. Calling attention to the many stark contrasts between himself and his opponent often brings out the best in the Republican presidential hopeful.

I don’t know whether involving Paris Hilton— as the McCain campaign recently did to the delight of late-night pundits everywhere — is always the answer, but if voters don’t know what you support and oppose, and how you are different from your opponent, they’ve got no good reason to vote for you and against him. Without facts, both positive and negative, there is no true choice.

So McCain should continue to make ads about policy, about funding for troops, and taxing and spending. The McCain campaign should make clear the differences between the Arizona senator and Obama. (On abortion, specifically; Obama wouldn’t oppose infanticide in the Illinois State Senate.) McCain should continue to use humor, to be a happy warrior, even as he forthrightly criticizes Obama. He should seek to drive home the biggest difference between the candidates: Their stances on the unpopular war in Iraq.

The “maverick” McCain should be bold enough to go negative. And then voters will know the truth. And that’s always a positive.

Kathryn Lopez is the editor of National Review Online. She can be contacted at klopez@nationalreview.com.