Here’s a nightmare question plaguing the dreams of Democrats.

Does John Kerry in a swift boat equal Michael Dukakis in a tank?

I know one was real and one pretend; one looks the part and one did not; and neither has anything to do with issues that ought to decide who runs the country.

But, I gotta tell ya, the longer the race for president mires in details of wartime incidents more than a quarter-century old, the more the incumbent is saved from accounting for details of his incumbency.

And it ain’t no accident.

“Bully for them,” a Democratic insider admits.

George W. Bush & Co. fueled a debate about who did what in a swift boat in Vietnam in the 1960s and about Kerry’s war decorations that, regardless of the truth, distracts media and voters from issues such as Iraq and the economy.

“It depends when and how it ends,” says Brookings Institution senior fellow Tom Mann, “If the charges are overwhelmingly discredited and Kerry regains the offensive on Iraq and the economy, Bush loses, not gains. But if they are allowed to fester ambiguously and indefinitely, then the smear will have worked.”

So far, it’s working.

The very war-hero element used to project Kerry as a capable leader in the war on terror now is muddied.

Take Bob Dole’s comments Sunday on CNN’s “Late Edition.” He said Kerry got an early exit from Vietnam because of “superficial wounds … three Purple Hearts and never bled that I know of.”

Ouch. This from a decorated WWII vet whose combat wounds cost him the use of his right arm.

Dole, the ads, et al, at the very least, cloud the air.

Which is astounding.

Does anyone doubt Kerry served in combat under fire?

Does anyone doubt Bush used name and connections to avoid combat?

Does anyone doubt links between anti-Kerry ‘Nam stuff, Bush supporters and Karl Rove?

Yet because Kerry was slow to respond (as was, I’d remind you, Dukakis in ’88), hoping, I assume, not to give the story legs, the story has legs.

And while the Kerry camp now is in full response — including a two-day, six-stop Pennsylvania fly-around by a Vietnam crewmate — again, the truth isn’t the issue.

The issue is the raw strategy of forcing attention away from vulnerabilities of the incumbent, which is to say Iraq, job loss, the environment, foreign affairs, “uniter not a divider,” take your pick.

That strategy accrues to Bush and hurts Kerry.

Now Bush wants it both ways. Monday, he decried swift boat ads and all such ads (“I’m denouncing all the stuff”) and said they should not air and Dole and others should stop.

This is a lame, after-the-damage offering, akin to saying “I condemn that unfair blind-side attack that did just what it was intended to do.”

Bottom line?

Catholic University politics professor John Kenneth White agrees with Mann that if the air clears completely, if there’s no doubt attacks on Kerry are baseless, Bush looks bad.

But, he also says, “This election could be won/lost in August.”

I’m not sure when the election is won and lost, but I am sure the air’s not clear yet, and August is slipping away.

John Baer is a columnist for the Philadelphia Daily News. His e-mail address is baerj@phillynews.com.