Some conservative activists have raised the prospect of a third party candidate in next year's U.S. presidential election if former New York City Mayor Rudy Giuliani becomes the Republican Party nominee.  In the fifth and final part of his series on the 2008 election, National correspondent Jim Malone looks at the possibility of one or more major third party candidates making a run for the White House next year.  

It does not happen often, but every once in a while a third party candidate has had an impact on U.S. presidential politics.

Larry Sabato directs the Center for Politics at the University of Virginia.

"Look at American history.  We have third party candidates that are significant about once every five elections," he noted.  "Now we had a very significant independent in 1992, Ross Perot.  We had a minor third party candidate who determined the result in 2000, Ralph Nader.  He gave the election from Al Gore to George W. Bush.  He tilted both Florida and New Hampshire to Bush.  All Gore needed was one of those two states to win.  So, even minor third party candidates can determine the results of a presidential election."

Some moderates believe there might be an opening for a centrist third party candidate next year if both major political parties nominate polarizing candidates who appeal to the extreme right and extreme left.

Hamilton Jordan served as President Jimmy Carter's White House chief of staff.

He is now involved in a centrist effort called Unity '08 that seeks to offer a bipartisan presidential ticket in next year's election.

"We are people that are not satisfied with the current political system, not satisfied with the status quo and are working to offer the American voters an alternative in 2008," he said.

The problem, according to Professor Sabato, is attracting the right kind of candidate to make a third party bid.

"You have to have somebody who is willing to run, who is well known, who has political experience, and who either has personal money or access to a lot of money to make a serious run at a third party or independent bid," said Mr. Sabato.

Even then, the chance of actually winning the election seems remote.

Former House Speaker Newt Gingrich recently decided against a bid for the Republican Party's presidential nomination next year.

"With the singular exception of Theodore Roosevelt, no third party candidate since the 1850's has had a serious chance of winning," he noted.

Some social conservative leaders have raised the possibility of running a third party candidate if Rudy Giuliani is the Republican Party nominee.  They disagree with Giuliani's support for abortion rights, gay rights and gun control.

Georgetown University political expert Stephen Wayne says that could be bad news for the Giuliani campaign.

"That candidate will only do well in rural and Republican areas, which will hurt Giuliani," he said.  "I think the idea of running an independent candidate was an attempt to stop Giuliani.  But I do agree with the general feeling that a third party, Christian right candidate is going to take votes away from Giuliani."

American University analyst Allan Lichtman thinks otherwise.

"Social conservatives have been threatening that for decades and it has never manifested itself," he said.  "They had a chance when [conservative] Pat Buchanan ran as the Reform Party nominee, but he got less than one percent of the vote and was an absolutely non-factor in the election."

Some Democrats are concerned that New York City Mayor Michael Bloomberg might launch an independent bid for the White House next year, possibly drawing enough votes away from the Democratic candidate to swing the election to the Republican nominee.

Bloomberg has appeal for moderates from both political parties.  But analyst John Fortier of the American Enterprise Institute sees little opening for a Bloomberg candidacy.

"Democrats are pretty happy with their candidates," he explained.  "Many of those states in the Northeast are pretty safely Democratic.  I do not see a lot of longing for Michael Bloomberg to get in the race."

While the likelihood of a well-known third party challenge in 2008 seems remote, plenty of other smaller parties will offer presidential candidates including the Constitution Party, the Green Party, the Libertarian Party and the Socialist Party.