On health care, Democrats are growing more optimistic that they can find a compromise approach to creating a government-run insurer to compete with the private sector  an issue that as much as any other has split the party’s liberals and moderates  even as progressive voices outside of Congress insist that there be no compromise.

“The fact is that Earl Blumenauer could stop a bill going through that does not have a public option in it,” said Jane Hamsher, founder of the progressive blog firedoglake.com. “Is it his loyalty to the party, partisan politics over principle? We are going to get to see that.”

Mr. Blumenauer strongly favors a public option and in late July was one of more than 60 Democrats who signed a letter to the leadership saying that, essentially, they would not back a final bill without an acceptable public plan. But on health care  as on other domestic issues, global warming and foreign policy  he must weigh whether it makes more sense to take what he can get as opposed to standing firm and perhaps seeing the overall effort collapse.

“It would be very hard for me to do,” Mr. Blumenauer said of voting for a final health care overhaul without a public plan. “But if it gets to the point where the choice is doing some things that will make a significant difference without a public option or letting the whole thing die, that too would be hard.”

Image Representative Earl Blumenauer with two staff members, Larry Weinstock and Janine Benner. Credit... Stephen Crowley/The New York Times

Mr. Blumenauer got on board early with Mr. Obama after concluding that he offered the chance for a more decisive change in course than Hillary Rodham Clinton could provide. He first met Mr. Obama at the 2004 Democratic convention in Boston and endorsed him in late January 2008.

“There was something going on here, this guy has got some real capacity being able to, I think, connect, communicate,” remembered Mr. Blumenauer.