Facing an incumbent running as a "war president," John Kerry will be using the Democratic convention this week to put some shine on his national security credentials, one of his biggest weaknesses among voters.

As the convention kicked off Monday night, Kerry backers stressed that their man had the background and capabilities to be commander-in-chief.

"I'm here to tell you John Kerry has made a plan to secure our homeland," said Rep. Jim Turner, D-Texas. "He will secure our borders. He will make our vulnerable targets — nuclear and chemical plants, oil refineries — more secure."

Turner, the ranking member on the Homeland Security Committee, continued, "The cost of securing America is great, but the cost of failing to secure America is even greater."

Former Secretary of Defense William Perry (search) stressed that Kerry will do a better job than Bush in protecting the homeland in a way that won't alienate the rest of the global community.

"Based on his own service, John Kerry understands what our troops need ... we must isolate the terrorists, not isolate the United States," Perry said.

While on the campaign trail, Kerry and his supporters have argued that Bush has taken the country in the wrong direction by going into Iraq without more international support. The Democratic candidate, whose Navy service won him a Silver Star, a Bronze Star and three Purple Hearts,  has vowed to take a more diplomatic route in the future to garner more support for military action.

Referring to troops fighting wars in Afghanistan and Iraq as well as soldiers stationed elsewhere across the globe, Perry said Democrats would do a better job of protecting them.

"We must keep our military the strongest in the world ... our forces have been dangerously overstretched," he said.

The themes of strength, leadership and security are heavily stitched throughout the four-day gathering, beginning with the opening speaker, the Rev. David Alston (search), a gunner on Kerry's boat during the Vietnam War.

Even the party's platform is tailored to be muscular — with more than 100 references to "strong," "strength" or "strengthen."

But Kerry must first overcome the deficit he faces against President Bush among voters who see the current commander-in-chief as a better leader on national security issues. Part of the problem for Kerry is that members of his own party oppose the war in Iraq and several wanted a statement in the convention platform describing the Iraq war as a mistake.

Platform writers were able to hold their ground, but Kerry's vote for the war in Iraq and then his opposition to funding soldiers there — the same position held by his running mate John Edwards — shows how frustrated Democratic leaders are in deciding the best approach to eliminating terrorism, Republicans say.

"We expect you'll hear Democrats use the term 'strong leader' a lot this week," Republican National Committee chairman Ed Gillespie said at a news conference. "We don't think a strong leader would vote to send our troops to Iraq then vote to cut off their money."

For his part, Kerry said he voted against the $87 billion supplemental bill because it sacrificed money for health care and education and lacked "a real plan that protects the troops and makes America safer."

Bush delights in quoting the senator.

"Senator Kerry tried to explain his vote by saying 'I actually did vote for the $87 billion before I voted against it,"' Bush told a Republican gathering last week. "There's nothing complicated about supporting our troops in combat. Leaders need to stand behind our military, and back them up 100 percent."

But Democrats also say they have a candidate who can make the tough choices. Having served in Vietnam as a swift-boat captain, many of his crewmates offer testimonials about his bravery and decisiveness.

Democrats add that the administration is trying to scare voters with warnings of a possible election-year attack, and say the $95 million spent by Republicans for radio and television ads is merely an effort to divert voters away from Bush's own record.

"It's a clash between fear and hope, that's what this election is all about" said Iowa Gov. Tom Vilsack (search). "The Republicans, basically, they hope people go into that voting booth afraid. They do, they might vote for a sitting president."

Bush served in the Texas Air National Guard, but his military record has been the subject of much scrutiny.

"You don't avoid by every means possible the war of your generation" and then order troops into Iraq as president, former Sen. Max Cleland (search) said at a caucus of convention delegates who served in the military. "You don't create a shooting war and close VA hospitals."

According to polls, Bush is still vulnerable on the issue of Iraq. Support for Bush's handling of Iraq has slumped to the low 40s as American deaths climb past the 900 mark and congressional investigations undercut the rationale Bush used for the invasion.

"Kerry has to say something that will get people who are unhappy about this war — and it is the most important problem facing the nation to a plurality of Americans — to understand the way he's different than Bush on it," said Andrew Kohut of the Pew Research Center (search).

As a counterpoint to Kerry's message of strength, Republicans plan to release a 12-minute video Wednesday that they say shows him shifting positions on the two Iraq wars. Kerry voted against the first war and in favor of the second.

"One of the strongest responses to the case that John Kerry will make that he's a strong leader is his own words," said Republican spokesman Jim Dyke. "Those words tell us that he is a flip-flopper."

Fox News' Peter Brownfeld and Liza Porteus and The Associated Press contributed to this story.