Democrat John Kerry's presidential campaign is likely to get a boost with the selection of North Carolina Senator John Edwards as his vice presidential running mate. Public opinion polls showed Senator Edwards was the favorite among Democratic voters. But does a vice presidential candidate really have any impact on the election? In announcing Senator Edwards as his running mate Tuesday, John Kerry stressed that the two of them would work together to attract support from independent voters as well as Democrats.

"I am determined that we reach out across party lines, that we speak [to] the heart of America, that we speak of hope and of optimism and John Edwards will join me in doing that," he announced.

The selection of a vice presidential running mate is usually the first major decision for a presidential candidate, even though the choice often means little when the election is held in November.

One exception to that general rule came in the 1960 election when Democrat John Kennedy chose Texas Senator Lyndon Johnson as his running mate. The Johnson selection probably swung the state of Texas to the Kennedy campaign and helped put the young Senator from Massachusetts in the White House.

"Historically, vice presidential decisions have usually not been the critical moment in presidential campaigns," said Alan Lichtman, a presidential historian at the American University here in Washington. "But they have played in presidential campaigns. For example, in 2000 George W. Bush made a surprise pick when he picked Dick Cheney, who was not considered a very good politician. But Dick Cheney gave some weight and some substance to the Bush campaign and gave it a boost at a time when it needed it."

Historically, presidential candidates have tried to offer a geographically balanced ticket by picking a running mate from another part of the country. Senator Edwards is from the south while Senator Kerry comes from the northeast.

But in 1992, Democrats fielded a ticket of two southerners, Bill Clinton of Arkansas and Al Gore of Tennessee, and still won the election.

Former President Clinton told National Public Radio that he believes Senator Edwards could help make Senator Kerry competitive in the south, a stronghold for President Bush.

"He will appeal culturally to some people who feel that they do not know Senator Kerry as well yet," said Mr.Clinton. I think he will help him in a lot of southern and border states to be a more competitive candidate."

Historian Alan Lichtman believes Senator Edwards' reputation as an energetic, optimistic campaigner could also help the Democratic ticket.

"Look, people are not going to vote for the number two," he said. "They are not going to vote for the vice president. But, John Edwards is good enough to give a real jolt of electricity to the Kerry campaign and maybe get it moving."

Despite the addition of Senator Edwards to the Democratic ticket, most analysts believe Senator Kerry has only a slim chance of carrying Senator Edwards' home state of North Carolina.

Senator Edwards was one of John Kerry's competitors for the Democratic presidential nomination until he withdrew in March. University of Virginia political expert Larry Sabato says the Republicans will likely focus on Senator Edwards' relative lack of experience in government, having served only one term in the Senate.

"Undoubtedly, the Republicans are going to dredge up Kerry's comments about Edwards and Edwards' comments about Kerry," said Mr. Sabato. "Kerry particularly noted the fact that Edwards was trying to jump in line [in running for president] and had very little experience."

In the short term, the Edwards selection is likely to further energize Democratic voters already mobilized to go out and vote against President Bush in November. But history suggests that it will be issues like Iraq and the economy and the character of the two presidential candidates that will have more impact on the outcome of the election in November.