PORTLAND, ORE. - In the breathless weeks before the Oregon presidential primary in May, Martha Shade did what thousands of other people here did: She registered as a Democrat so she could vote for Sen. Barack Obama.

Now, however, after critics have accused Obama of shifting positions on issues like the war in Iraq, the Bush administration's program of wiretapping without warrants, gun control and the death penalty -- all in what some view as a play to a general election audience -- Shade said she planned to switch back to the Green Party.

"I'm disgusted with him," said Shade, an artist. "I can't even listen to him anymore. He had such an opportunity, but all this 'audacity of hope' stuff, it's blah, blah, blah. For all the independents he's going to gain, he's going to lose a lot of progressives."

For all the idealism and talk of transformation that Obama has brought to the Democratic Party, there is also a wide streak of pragmatism, even among many grass-roots activists, in a party long vexed by factionalism.

"We're frustrated by it, but we understand," said Mollie Ruskin, 22, who is spending the summer with a nonprofit that trains young people to campaign for progressive candidates. "He's doing it so he can get into office and do the things he believes in."

Still, others warned that Obama risked being viewed as someone who parses positions without taking a principled stand.

"I'm not saying we're there yet, but that's the danger," said David Sirota, a liberal political analyst and author. "I don't think there's disillusion. I think there's an education process that takes place, and that's a good thing. He is a transformative politician, but he is still a politician."

Joe McCraw, 27, who writes three liberal blogs, said Obama's shift on the domestic spying measure was a watershed moment. "This is the first time I've ever seen him lie to us, and it makes me feel disappointed," McCraw said.

HEY, THAT'S NOT FUNNY: Comedian Bernie Mac received a campaign rebuke during an appearance Friday night at a fundraiser for Obama, The Associated Press reported.

Toward the end of a 10-minute routine at the Hyatt Regency Hotel in Chicago, the star of "The Bernie Mac Show" joked about menopause, sexual infidelity and promiscuity, and used occasional crude language.

Minutes later, Obama tried to smooth things over.

"We can't afford to be divided by race. We can't afford to be divided by region or by class and we can't afford to be divided by gender, which by the way, that means, Bernie, you've got to clean up your act next time," Obama said. "This is a family affair. By the way, I'm just messing with you, man."