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 Senator Barack Obama.

Now, however, after critics have accused Mr. 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 shameless play to a general election audience  Ms. Shade said she planned to switch back to the Green Party.

“I’m disgusted with him,” said Ms. 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.”

Of course, that depends on how you define progressives.

As Ms. Shade herself noted, while alarm may be spreading among some Obama supporters, whether left-wing bloggers or purists holding Mr. Obama’s feet to the fire on one issue or another, the reaction among others has been less than outrage.