STAR POWER He's got it, she doesn't. Annie Marie Musselman

It was supposed to be a pep rally, an election-year excuse for getting Washington State's junior senator, Maria Cantwell, on stage with one of the Democrats' most popular figures, Senator Barack Obama of Illinois. The advance press materials said the topic of the day was education, but for a few tense minutes on Saturday, the otherwise well-scripted Cantwell campaign event was upended by an antiwar ambush.

Protesters unfurled a smuggled-in banner that read "Maria Can't Say No to War," and began shouting at Cantwell just as she rose to address the large crowd in the Garfield High School gym. The senator tried to talk over the protesters, but appeared both flustered by their interruption and embarrassed at having brought her superstar Senate colleague all the way across the country just to suffer an uncomfortably off-message moment.

King County Executive Ron Sims jumped in, rescuing the floundering senator by leading the audience in a counter-chant of "Cantwell, Cantwell." But as Cantwell's handlers worked to hustle the protesters out of the gym, it became clear that the woman who won her Senate seat by a slim margin in 2000 has a Seattle problem on her hands as she tries for a second term.

The problem is an outgrowth, in part, of the problem Cantwell has had for some time among liberals as a result of her 2002 vote to support the U.S. invasion of Iraq. While prominent Democratic senators like John Kerry and John Edwards have since described their votes for the invasion as a mistake, Cantwell has been unapologetic, at times mimicking the Bush administration's rosy talking points on the war.

Recently, she's managed to upset environmentalists, too, by embracing the appointment of Republican eco-nemesis Dirk Kempthorne to the post of interior secretary. "We were disappointed," said Mike Palamuso, Northwest campaign manager for the League of Conservation Voters, speaking of Cantwell's support for Kempthorne. While Palamuso's group has endorsed Cantwell's campaign and given her near-perfect marks on the environment, it has given Kempthorne a dismal lifetime environmental score of 1 percent.

Alienating peaceniks and environmentalists doesn't seem like a good strategy for rallying the huge liberal base in King County, which holds the biggest trove of voters in the state, and Cantwell's campaign appears to have realized this.

"Senator Cantwell, having won her first election by less than 2,500 votes, understands the importance of King County voters and will work tirelessly for each and every vote," Cantwell campaign manager Matt Butler told The Stranger a few days after the Garfield event.

However, with Cantwell facing a recently announced challenge from the left by antiwar Green Party candidate Aaron Dixon, and from the right by Republican former insurance executive Mike McGavick, the question is how many Seattle liberals Cantwell has already lost.

"I think she's taking some risks," said Jill Wasberg, spokeswoman for the Washington Conservation Voters. "I think she needs to remember who her base of voters are in Seattle."

Butler defended Cantwell's environmental record and her Iraq stance, saying she has been "demanding accountability by the Bush administration on the war." But he wouldn't say whether Cantwell would join Kerry and Edwards in repudiating her vote to start the war in the first place.

It remains to be seen how widespread the sense of disenchantment with Cantwell really is among hardcore Seattle liberals, and whether it will matter come November. A recent Rasmussen poll shows Cantwell with a healthy 13-point lead over McGavick, and Democratic pollster Don McDonough says mass liberal defections in King County are unlikely.

"I'm not saying that there's not a certain small sliver of liberals that won't vote for her," he said. "But it's not going to be the most significant factor in the race."

McDonough said he does find it "somewhat inexplicable" that Cantwell won't mollify her angry antiwar constituents by saying her vote for the war was a mistake, but he also said he's paying more attention to President Bush's approval rating, which he sees as the prime indicator in the race.

The president's approval rating has been hovering around 35 percent lately, and McDonough said that for every point below 40 percent that Bush is in November, Cantwell will gain a point against her main challenger, Republican McGavick.

eli@thestranger.com