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Sen. John McCain defended his support for the Iraq war Tuesday in a commencement speech at Columbia University that had been expected to draw boisterous protests from student activists.

But a driving rainstorm dampened much of the expected activity, forcing the 1,064 graduates to listen to the speech shivering under umbrellas or in makeshift raincoats made of trash bags.

The Arizona Republican addressed Class Day at Columbia College, the university's liberal arts undergraduate division, where his daughter, Megan, is a junior. Commencement exercises for the full university take place Wednesday.

Dressed in a black academic robe with a deep blue sash, McCain managed to stay somewhat dry on a tented stage. He reiterated his belief that the Iraq conflict was just, but he encouraged those who disagreed to say so loudly and forcefully.

"Americans should argue about this war. It has cost the lives of nearly 2,500 of the best of us," McCain said. "If an American feels the decision was unwise, then they should state their opposition and argue for another course. It's your right and your obligation."

McCain, who is widely expected to seek the GOP presidential nomination in 2008, insisted the war was not simply a campaign to spread American pop culture or consumerism around the globe. Instead, he called it a concerted effort to extend human rights and freedom to persecuted peoples.

He also drew a distinction between American values and those of Islamic extremists, pointing to the genocide in the Darfur region of Sudan, where Osama bin Laden has threatened violence against Westerners who dare to intervene.

"Now that, my friends, is a difference, a cause, worth taking up arms against," McCain said.

The 15-minute speech was nearly identical to the address McCain delivered at Rev. Jerry Falwell's Liberty University in Lynchburg, Va., last Saturday, just shaved a bit for length, said his political adviser John Weaver.

Indeed, it was McCain's decision to address Liberty — along with his support for the war and opposition to gay rights and legal abortion — that originally spurred the protest effort on Columbia's campus.

As visitors streamed toward the seating area, activists distributed bright orange fliers proclaiming "John McCain does not speak for us." Dozens of students wore orange buttons bearing the same message pinned to their graduation robes, but the deluge meant most of the buttons ended up covered by rain gear.

Likewise, the centerpiece of the protest, where students stood during McCain's speech and opened orange and white umbrellas bearing anti-war slogans, was something of a washout. Only about two dozen students opened the protest umbrellas, and they were nearly obscured by the hundreds of other umbrellas students were using simply to stay dry.

"It was total chaos," acknowledged Kim Sue, a graduating senior who helped organize the protests.

But, Sue said, the overall effort was positive.

"We wanted to show there was opposition at Columbia, and that we would not go quietly and just listen to McCain," Sue said. "He's so well respected as a veteran and war hero, he could use that reputation for peace. And he just doesn't."

Protests are expected at another New York commencement Friday, when McCain is scheduled to speak to graduates of The New School.