One key point I should have made earlier: actually claiming credit and getting people to believe it is an important political skill, one that liberal activists now show that they have mastered (see, for example, this Sullivan post). Good job, liberal activists!
I guess I should add two things. First, I think it's a major stretch to say, as Nate Silver does, that the fight over public option is important because of "paradigm-shifting implications it could have for how business gets done in the Democratic Party." I don't think things work that way; politicians are going to follow all their incentives, and Democratic Senators from states such as Arkansas, Louisiana, and North Dakota are always going to tend to follow the median voter in those states -- or else they aren't going to stay in the Senate very long. Liberal enthusiasm and toughness can't change the basic incentives faced by Lincoln and other swing-state Senators.
However, that doesn't mean that liberals shouldn't fight hard for what they want, as long as they avoid doing the sorts of destructive things that conservatives are doing to the GOP in the New York this week. And claiming credit successfully, deserved or not, can make a difference -- not by "paradigm shifting," but around the margins. After all, Newt Gingrich is still getting mileage out of his successful (albeit almost entirely false) claim of credit for the 1994 elections.