Arizona Sen. John McCain (search), arguably the Democrats' favorite Republican, rejected the notion that John Kerry (search) is weak on defense Thursday.

President Bush and his campaign apparatus have gone to great effort to suggest the Democratic presidential contender would be an unfit commander in chief, picking apart his Senate voting record on weapons and defense spending.

"The senator from Massachusetts has given us ample doubts about his judgment and the attitude he brings to bear on vital issues of national security," Vice President Dick Cheney (search) declared Wednesday. A day earlier, the Bush campaign released an ad arguing Kerry had turned his back on U.S. soldiers by voting against an $87 billion aid package for Iraq and Afghanistan last year. On Thursday, the campaign put out yet another ad accusing Kerry of waffling on military issues.

Enter McCain.

Asked on two morning TV shows Thursday whether he thought Kerry was weak on defense, the Arizona senator was quick to bat down the suggestion. Furthermore, he chided both parties for waging such a "bitter and partisan" campaign.

"This kind of rhetoric, I think, is not helpful in educating and helping the American people make a choice," he said.

As for Kerry, McCain said the senator would have to explain his voting record. But he also said: "No, I do not believe that he is necessarily weak on defense. I don't agree with him on some issues clearly. But I decry this negativism that's going on on both sides."

It's not first time the independent-minded McCain has strayed from the Republican line.

"He doesn't usually pick up the president's talking points and amplify them," said James Thurber, a political scientist at American University. "He speaks his mind."

That's just the quality that Democrats find so endearing.

In fact, when the Democratic presidential contenders were asked earlier this year to name their favorite Republican, four of the nine — including Kerry — selected McCain. He was the only one to be named more than once.

For McCain, talking about Kerry is not just business, it's also personal.

The two are good friends, a somewhat unlikely destination given their histories.

McCain, a Navy bomber pilot, spent more than five years as a prisoner of war in Vietnam. Kerry, who also served in the Navy during Vietnam, came home with three Purple Hearts and a Silver Star and became a leader of Vietnam Veterans Against the War (search). At one protest in 1971, he threw away war medals belonging to other veterans and cast his own military ribbons over a fence. McCain heard about it while he was still being held captive in the Hanoi Hilton.

After McCain was elected to the U.S. House, he campaigned against Kerry in his first Senate race, faulting him for tossing away those medals and ribbons. But the two came to terms after they got to the Senate, and began working together. It was McCain and Kerry, for example, who pushed to end the trade embargo on Vietnam and to establish diplomatic relations with the country.

McCain has described their current relationship as "easy."

"I think it's still possible to have a friend if they're in another party," he said Thursday.

The Kerry campaign welcomed McCain's comments, noting that the Arizona senator has been a leader on defense issues for decades.

"It's helpful to our campaign, but it's also helpful because it speaks the truth," said Kerry spokeswoman Stephanie Cutter.

Bush campaign spokesman Terry Holt said McCain was right — at least when he said Kerry would have to explain his voting record.

"As John McCain indicated, the record is appropriate to discuss and the record clearly suggests that John Kerry is weak on national defense," Holt said.

McCain has campaigned for Bush this year, but the two are not considered close, especially since the 2000 presidential race, when McCain and Bush competed for the GOP nomination. Bush's supporters waged a particularly negative campaign against the senator.

McCain "hasn't forgotten that," said Thurber. "But I don't think he's out to get him. He's just an independent-thinking Republican."

McCain said last week he would consider an offer from Kerry to be his running mate, but his office later issued a statement reversing course.

On Thursday, McCain said he didn't want to be vice president on either party's ticket.

"N-O," he said.