John Kerry (search), a confident front-runner in the race for the Democratic nomination, vowed Monday to stand up to the Republican Party and its "culture of fear" and questioned whether rival John Edwards (search) could carry his own state against President Bush.

Kerry trailed Edwards, a North Carolina senator, in the latest polls taken in the South Carolina primary, which Edwards has said he must win in his bid for the nomination. Kerry, a Massachusetts senator, led in polls taken in five other states holding delegate elections Tuesday and was virtually tied in another, Oklahoma, with Wesley Clark (search).

"We're not going to convince the South or any other part of the country that we Democrats know how to keep America safe unless we can stand up to him -- Bush -- on national security," Kerry said in a satellite interview with South Carolina television stations. "I have a 35-year record of fighting for my country, fighting in a war, fighting against a war. This is not the time for on-the-job training in the White House on national security issues."

In between interviews, Kerry told an aide: "Edwards says he's the only one who can win states in the South. He can't win his own states." A Kerry aide later said the remark was in response to public polling showing Bush winning North Carolina in the November election.

In response, Edwards said: "I am the only Democratic presidential candidate in the field who has a proven record of being able to win the type of tough states Democrats will need to win in the general election and I will do it again tomorrow."

"I think it's important that voters understand when we talk about electability that I am the only candidate that actually has a record of having won in a tough state," he said, referring to his defeat of an incumbent Republican senator in 1998.

Meeting with reporters as he arrived in Tucson, Ariz., Kerry refused to associate himself with disparaging remarks some of his big supporters have made about Bush's military service. Democratic National Committee Chairman Terry McAuliffe (search) said Bush was "AWOL" during the Vietnam conflict, while former Sen. Max Cleland of Georgia has criticized Bush's service in the Texas Air National Guard.

"I've never questioned the choice people made in not going to Vietnam," Kerry said.

Speaking earlier to a rally at the University of New Mexico, Kerry told about 300 backers, "I predict today, like father like son, one term only, Bush is going to be done."

Riding high following back-to-back wins in Iowa and New Hampshire -- and upbeat about his prospects in the states with elections Tuesday -- Kerry was largely ignoring his Democratic rivals to focus on the Republican incumbent. The decorated Vietnam War veteran sought to make the case that, among the Democratic hopefuls, he was best qualified to answer the GOP on national security.

"That's what they do best is spread the culture of fear," the four-term Massachusetts senator said. "I'm not going to let them put the Democratic Party or any American on the defensive about asking legitimate questions about how we make our nation strong."

Edwards on Monday criticized Kerry's acceptance of contributions from lobbyists, his record on trade and his years as a Washington politician. Howard Dean also assailed Kerry about donations from lobbyists.

Countering the special interest criticism, Kerry was joined on the campaign trail by New York State Attorney General Eliot Spitzer, who has captured national headlines for his battles against Wall Street.

In an interview, Spitzer said of Kerry: "With his long record of standing up for all Americans against special interests, John Kerry is the best candidate for president."

Kerry also picked up new endorsements from labor unions and congressional Democrats, a reflection of the party establishment moving toward the front-runner.

The National Treasury Employees Union represents about 150,000 workers in 29 government agencies, while the Sheet Metal Workers International Association represents about 150,000 skilled craftspersons in the unionized sheet metal industry.

Added to his other organized labor endorsements, Kerry now has the support of unions representing more than 1.3 million workers.

Among members of Congress, Washington Sen. Maria Cantwell endorsed Kerry on Monday, along with Colorado Rep. Mark Udall and Texas Rep. Ruben Hinojosa, the 35th House member to back him.

Kerry was joined by New Mexico Gov. Bill Richardson, who has not endorsed a candidate but whose presence was a boost for Kerry among Hispanics, a key constituency.