As is the case with beauty, wit and cuisine, negative politics occurs in the eye of the beholder, or in this case, the voter.

The 2008 presidential campaign has turned rough, which is no surprise in an election where so much is at stake. This week’s Exhibit A was Massachusetts Sen. Edward Kennedy’s endorsement of Sen. Barack Obama for president over Sen. Hillary Rodham Clinton.

Kennedy’s move was motivated, at least in part, because he was upset with negative shots at Obama taken by former President Bill Clinton on behalf of his wife’s campaign.

Politics, as writer Peter Finley Dunne said, “ain’t beanbag.”

In the world’s greatest democracy, campaigns have a long history of nastiness, character assassination and even violence, most famously in 1804, when Aaron Burr killed Alexander Hamilton in a duel that arose from a campaign for New York governor. The sleazy tactics used by supporters of George W. Bush on Arizona Sen. John McCain in 2000 in South Carolina — which included charging that McCain had fathered a black child out of wedlock and was an alcoholic — are legendary.

As was the infamous 1988 Willie Horton ad aimed at Michael Dukakis’ presidential campaign and the 2004 Swift Boat television ads twisting John Kerry’s Navy service in Vietnam.

Yet, voter reactions to political campaigns change over time; the political zeitgeist may be the biggest factor in whether an attack is considered outside the boundaries of proper discourse.

Bill Clinton set the Democratic campaign boiling in a televised remark Saturday in which he tried to marginalize Obama as a black candidate, saying a victory over his wife by the Illinois senator in South Carolina would have no more impact on the presidential campaign than the Rev. Jesse Jackson’s victories in South Carolina in 1984 and 1988.

Clinton earlier called Obama’s opposition to the Ira q war a “fairy tale.”

“I think it was pretty mild compared to what we have seen in the past,” said Dotty Lynch, the longtime senior political editor for CBS News who now teaches political science at American University.

“But this year the rules of engagement may have changed and that may have caught up to Bill Clinton,” said Lynch in an interview. “When you look at something like the South Carolina attacks, that may have been perceived by many people as highly negative and out of bounds.

“I do think the injection of the race and gender issues may have had something to do with the South Carolina results. It may have been enough to move black voters,” said Lynch, referring to the jaw-dropping landslide Obama claimed over Hillary Clinton in that state.

Academics and those who work in politics have argued for years about the impact of negative campaigning. Candidates use it because it works; various studies show that voters remember negative television ads more than positive advertising.

There is a dispute among experts about the ultimate effects of negative campaigns on the electorate.

Some studies that show that nasty campaigns tend to turn off voters and depress voter turnout. Other studies by political scientists say the opposite, that negative campaigns engage voters and lead to more participation.

Shanto Iyengar, of Stanford University, has studied negative campaigns extensively and has concluded that they turn voters off.

“It is a question of what are you going negative on,” said Iyengar. “No one would have raised a finger if (Bill Clinton) had attacked Obama’s health-care plan as not being comprehensive enough. But the racial stuff and the Jackson comment was just way over the line. I think Senator Kennedy is in line with what most people think about that stuff.”

Negative campaigning is always intertwined with campaign strategy, says Tobe Berkovitz, a political communications expert at Boston University.

The Clinton campaign was content to play nice with Obama, Berkovitz says, until Obama won the Iowa caucuses and became a threat to Senator Clinton’s quest for the White House.

“Hillary Clinton has from the start played the gender card, saying her election would be historic for women,” said Berkovitz. “But as soon as Obama started succeeding, the Clintons decided they would no longer take the high road.

The tactic is often to use mudslinging to drag the opponent into the muck, put him or her on the defensive and make the opponent get down and dirty to defend themselves, said David Proctor, a Kansas State University expert on negative campaigns.

“The idea is to get voters to think all politicians are slimy people who will say anything to get elected,” said Proctor. “The Clintons are masters at this sort of politics in that they are always thinking about strategy and tactics and whatever they have to do to build a coalition to get 51 percent of the vote.”

One certainty about negative campaigning, says Professor Joanne Free man of Yale University, is that it’s always been part of the American political landscape and will never end.

“This stuff has always been around. In 1800, John Adams’ campaign spread rumors that Thomas Jefferson was dead,” said Freeman. “If you have democratic elections, you are going to have dirty campaigns.”

(Reach Scott Mackay at smackay(at)