Political signs are stolen or vandalized every election cycle, but many campaign officials and political historians say this year is different.

"I think this [presidential] campaign ranks at, or near the top of, dirty campaigns post-World War II," said Allan J. Lichtman, a presidential scholar at American University.

Sign snatchings have been reported in Maryland, Virginia, West Virginia and Pennsylvania, as well as the home states of President Bush and Sen. John F. Kerry, according to police, newspaper and television reports. Theft also has been reported in Florida, Tennessee, South Dakota, Wisconsin and Washington, Oregon and Ohio, Kentucky and Colorado, Minnesota, Missouri and Michigan.

In some battleground states, the thievery has been on a grand scale.

Nearly 500 Bush/Cheney yard signs were pilfered from neighborhoods in York, Pa., in late August and early September, Republican Party officials there said, including a 6-by-8-foot banner taken from the downtown Bush/Cheney headquarters.

About 350 Kerry/Edwards yard signs were stolen or vandalized in late August in a Republican region of Pensacola, Fla., known there as "Bush Country." Kerry supporters responded quickly by hanging more signs from high tree limbs, the Pensacola News Journal reported.

Presidential historian Richard Shenkman says the spontaneous outbreak of vandalism across the country is the inevitable venting of high temperatures in a rambunctious campaign -- temperatures that are coming to a full boil as the election nears.

"Any time you've got a divided country, that divisiveness just gets the blood going of these very competitive people who are in the business of getting their candidate elected, and then you tend to have more ugly politicking and smear campaigning."

Lichtman says he thinks the dirty campaigning is a result of polarized, dug-in parties more than a polarized country.

"The country was much more polarized during the '60s, or the Civil War for that matter, or during the run-up to World War II," Lichtman said. "What you've never seen in modern history are parties that are more polarized. . . . The parties are cleanly split and it's getting worse."

Shenkman and Lichtman say they think this campaign is uglier than recent campaigns because negative electioneering tactics and dirty political trickery spread across the country with much more velocity now through new types of media.

"We have a tradition of ugly politics in America," said Shenkman, author of "Legends, Lies and Cherished Myths of American History." "But this campaign is much more intense because of the Internet, 24-hour cable news and talk radio. There are so many more ways to communicate smears. It's all smear all the time."

As Exhibits A through C, he cites:

* The flood of media coverage about documents questioning President Bush's National Guard service, documents that most experts say were probably faked.

* The widely reported but unsubstantiated attacks on Kerry's record in the Vietnam War by the Swift Boat Veterans for Truth.

* Widely circulated e-mail warnings of a possible military draft if Bush is re-elected.

But can dirty campaign tactics and tricks make a difference in a presidential election?

"There's no question they are making a difference," Shenkman said. Kerry received no post-convention "bounce" in the polls because of the timing and effectiveness of the anti-Kerry Swift Boat ads and consequent media coverage, Shenkman said, even though none of the ad's claims about Kerry's actions has been corroborated.

"It is unprecedented for a candidate not to get a bounce after a political convention," he said.

Shenkman cites a presidential campaign in which a dirty campaign trick decided the election.

In 1888, when President Grover Cleveland was running for re-election, one of the most important ways for a candidate to win the Irish vote in the swing state of New York was to distance himself from Britain. Just a few weeks before the election, a letter surfaced that had been sent from the British ambassador in Washington to Charles Murchison, supposedly an Englishman living in California. In the letter, the ambassador endorsed Cleveland.

"That was the kiss of death," Shenkman said. Irish voters abandoned Cleveland in droves and he lost the White House.

After the election, it was revealed that the "Englishman" who wrote the ambassador asking his presidential preference was a California Republican. Cleveland had been undone by a dirty trick.