DENVER -- Four years ago, Sen. John Kerry took the stage on the fourth night of the Democratic National Convention in his hometown of Boston, saluting the crowd as he accepted his presidential nomination and announcing he was "reporting for duty."

It wasn't to be.

Kerry lost a tight election to President George W. Bush and now faces his first primary challenge in 24 years since becoming a Massachusetts senator. He also has a Republican opponent serious about unseating the man who was almost president as he seeks a fifth term in the Senate.

"In 2004, we came so close to victory. We are even closer now, and let me tell you, this time we're going to win," Kerry said last night from the podium of the Pepsi Center, playing a significantly different role at this year's convention.

Kerry spoke shortly after former President Clinton, his wife, Theresa Heinz, in the audience, seated next to Michelle Obama.

In an address that focused on national security, Kerry blasted the Bush administration for "squandering" America's stature in the world and replacing diplomacy with party ideology. He also defended Barack Obama against charges that the Democratic nominee lacks patriotism.

"George Bush, with John McCain at his side, promised to spread freedom, but delivered the wrong war in the wrong place at the wrong time. They misread the threat and misled the country," Kerry said, reprising a theme from his presidential campaign.

Times have changed in four years for Kerry, who has spent much of his summer traveling in Massachusetts, trying to deflect criticism that he has often been more focused on national concerns than his home state.

"I was proud of him," said U.S. Rep. Jim McGovern, a Worcester Democrat, after the speech. "I think he would have been an incredible president, and I think the country lost out."

In Denver, Kerry once again had the ear of the national public, and he used it to make the case that Obama not only has the judgment necessary to lead the country, but the temperament to respond like "a statesman of the 21st century."

"When Barack Obama promised to honor the best traditions of both parties and talk to our enemies, John McCain scoffed," Kerry said. "George Bush called it 'the soft comfort of appeasement.' But today, Bush's diplomats are doing exactly what Obama said -- talking with Iran."

Kerry's Republican opponent in Massachusetts, Jeff Beatty, a former Army Delta Force officer and CIA counterterrorism agent from Harwich, took a different view of Kerry's remarks, pointing out that Kerry himself voted to authorize the war in Iraq.

"I don't like the image of Barack Obama and John Kerry," he said. "To me, they represent a weaker America."

A three-time Purple Heart recipient for his service in Vietnam, Kerry also condemned what he called the same "Rove tactics" being used against Obama to question the nominee's patriotism that derailed his own presidential ambitions, referring to Republican operative Karl Rove.

Kerry, of course, was the subject of the now-infamous "Swift Boat" advertisements that successfully called his military service into question.

"No one can question Barack Obama's patriotism," Kerry said. "Like all of us, he was taught what it means to be an American by his family: his grandmother, who worked on a bomber assembly line in World War II, his grandfather, who marched in Patton's army, and his great uncle, who enlisted in the Army right out of high school at the height of the war."

Obama's uncle, in attendance last night, was pointed out for recognition by Kerry from the stage.

Kerry, along with his Senate colleague Edward Kennedy, came out early in the primary for Obama with an endorsement that helped give the young Obama campaign a boost.

With U.S. Sen. Joe Biden on the Democratic ticket for vice president, politicos can't help but wonder if Kerry might be on the top of Obama's list for secretary of state if Obama is elected.

Kerry has brushed those questions aside, calling it a "hypothetical" question and insisting he looks forward to another six years in the Senate.

When he gets there, he said he hopes to see the same McCain he has known for decades seated in the chamber, rather than the Oval Office.

"I have known and been friends with John McCain for almost 22 years," Kerry said. "But every day now, I learn something new about candidate McCain. To those who still believe in the myth of the maverick instead of the reality of the politician, I say, let's compare Senator McCain to candidate McCain."