John F. Kennedy said the Eisenhower administration presided over a lethal missile gap. Richard M. Nixon indicated he had a secret plan to end the Vietnam War. George H.W. Bush said he wouldn’t raise taxes. And the best of all of them: Jimmy Carter said he wouldn’t lie to us.

None of these statements turned out to be exactly right. No matter. All four presidential candidates — two Republicans, two Democrats — got elected.

So, too, might Sen. John F. Kerry. His commercials said President Bush favors sending American jobs overseas, which is almost certainly not true. Then again, the president’s campaign has said Kerry voted for higher taxes 350 times, which is not quite right either.

Presidents don’t always tell the truth, and candidates for president don’t either. “Nixon is a shifty, goddamn liar, and people know it,” Harry Truman said about one of his successors. He also said, about the same successor: “I don’t think the son of a bitch knows the difference between telling the truth and lying.” Plus this: “Nixon is a no-good lying bastard.”

But enough about Nixon, who hasn’t run for president for a third of a century. What is surprising is that the lies (and the little fibs) that candidates make often are taken at face value, even today.

Seeing is believing

The source for this distressing fact of political life is the University of Pennsylvania’s National Annenberg Election Survey, which in a study this month found that the public absorbs and believes a lot of what it hears on television commercials. In short, a lot of people believe a lot of that garbage you see on TV. Here’s the data:

Three out of five Americans in the 18 battleground states where the most political ads have been running believe that Bush favors sending American jobs overseas. (Reality check: Without job growth, the president may find himself out of a job.) More than half of Americans in those states believe Kerry has voted for higher taxes 350 times. (Reality check: Even Strom Thurmond didn’t live long enough to do that.)

The political professionals who produce negative ads know what they are doing, which is mostly to sow doubts in the minds of undecided voters and, just as important, to reinforce the prejudices of those who have come to distrust or dislike their opponents.

No one likes these ads, except of course the people who make them (and who, not coincidentally, profit whenever they are aired on television or radio). And yet no candidate dares campaign without them. They work. Often they work miracles.

They work because within them lies a speck of truth. They work because they have come to substitute for lengthier, more thoughtful critiques of the candidates. They work because they build on voters’ suspicions, voters’ worries, voters’ impulses.

Two examples: It’s plausible, though not true, that Bush, no enemy of corporate leadership, could advocate shipping American jobs overseas. It’s plausible, though not true, that Kerry, no enemy of taxes, could be a serial supporter of higher levies.

These ads exploit ambiguity, but their real power is that they exploit vulnerability. “Don’t give speeches that are pure bunk,” the late Speaker Thomas P. O’Neill Jr. of Massachusetts once wrote. Maybe not, but the speaker, who never adjusted gracefully to the television age, didn’t say not to underwrite campaign ads that are pure bunk.

Enter the ‘truth squad’

Not that those ads are risk-free. “Whenever you introduce falsehoods into a campaign, you gain short-term advantage, but you leave yourself open to being a liar,” says Stephen Steinberg, executive director of the National Commission on Society, Culture and Community, also at Penn. “That’s why truth-squadding has become so permanent.”

Indeed, candidates’ tendency to respond to their rivals’ parries has changed the entire routine and the entire tone of presidential politics. Just 16 years ago, Gov. Michael Dukakis of Massachusetts didn’t respond to the GOP’s charges about weekend furloughs, the Pledge of Allegiance, the cleanliness of Boston Harbor and the governor’s membership in the American Civil Liberties Union. Dukakis lost 40 states and the Democrats vowed never to let a campaign attack go unanswered again. John Kerry, tellingly, was Dukakis’ lieutenant governor, not his campaign manager.

The result: Today every charge begets a countercharge, almost always within the same news cycle. It’s an employment program for campaign aides but a confusing mess for the public.

More of this is on the way. The most recent Zogby International Poll shows Kerry with a five-point lead over Bush. Look inside the data and you will see that in the states that Vice President Al Gore won in 2000, Kerry is in robust shape, with a lead of more than 10 percentage points. In the states that Bush carried in the contested election four years ago, the two men are tied.

That’s a prescription for trench warfare, and perhaps for trench mouth. The two sides will fight fiercely. It is no coincidence that the word “campaign” is taken from the military. Ulysses Grant, for example, fought the Wilderness Campaign of 1864 before he gave any thought to contesting the presidential campaign of 1868. (He won both.)

The charges will fly like missiles or bullets or cannonshot. Choose any simile you like. There will be some hits, many misses, and the shame of it is that it may not matter if the charges are true. It’s the nature of warfare and of politics.

David Shribman is a columnist for Universal Press Syndicate.