Noam Scheiber confuses me

My specialty is in international relations and not American politics, so maybe that explains why I don't completely understand Noam Scheiber's op-ed in the New York Times on the implications of the end of Joementum: [T]here was a time when the support of key Democratic interest groups would have more than made up for such heresies. That he could not depend on that traditional lifeline this time should be alarming even for those who hoped for his defeat. Consider the way Democratic politics has worked for most of the last 40 years. If you were a Democratic member of Congress, pretty much the only way to earn yourself a primary challenger was to oppose a powerful local interest group on an issue it deemed critical. If you represented a Rust Belt district, for example, you could all but count on winning your party?s nomination every two years as long as you voted with the local union on trade legislation. Under this old model, Mr. Lieberman was an all-star. He was a reliable vote on what Connecticut liberals care about: defending the right to abortion, fighting oil drilling in the Alaskan Arctic, raising the minimum wage. When he did depart from Democratic orthodoxy, it usually involved attacking constituencies with little influence in his state, like Hollywood movie producers. But over the last six years this old model has broken down. As anyone who hasn?t been living in a cave knows, traditional Democratic interest groups have steadily lost ground to a more partisan, progressive movement skilled at using the Internet to communicate and raise money. The most visible faces of the new movement are the thousands of political bloggers ? and their millions of readers ? who delighted in panning Mr. Lieberman these last several months. But the movement also consists of national fund-raising and advocacy groups like MoveOn.org and Democracy for America (the current incarnation of Howard Dean?s 2004 presidential campaign). Call them the counter-Bushies, after the president whose singular talent it is to drive them to paroxysms of rage. What matters to the counter-Bushies is basically the opposite of what mattered to the traditional interest groups. The new gang doesn?t care so much about any one issue; it wants Democrats to present a united, and generally liberal, front. (According to a Pew Research Center survey released last year, more than 80 percent of Democracy for America supporters consider themselves liberal, versus less than 30 percent of all Democrats.) But to discuss the counter-Bushies? approach strictly in terms of substance doesn?t do them justice. Often they care as much about style as about issues ? they want Democrats to denounce Republicans loudly and stridently, and to block the administration?s agenda whenever possible. Oddly, a party in which the counter-Bushies have replaced the traditional interests may even move rightward in particular cases. Under the new model, for example, our old Rust Belt congressman can probably buck the local union on trade. But the changes do make the party more liberal over all, because our congressman must now make up what he lost in labor backing with support from the counter-Bushies. He can only do that by stridently denouncing the Republican Party and racking up a more liberal voting record. The flip side of this calculus for that Rust Belt congressman is that simply voting the right way on trade no longer suffices. Labor has lost the power to deliver him the nomination, just like it?s lost the power to sandbag him. Formally, Scheiber's argument has some logic -- if an interest group holds a veto over the nomination process, and they care only that their rep take position A* on issue A, then Congressman Smith can adopt any position on issues B-Z. If the netroots have veto power, Scheiber is arguing that Smith can adopt A' rather than A*, so long as he compensates by modifiying his positions on issues B-Z such that they conform to the base's preferences. There's only one problem with this argument, and it's contained within Scheiber's op-ed: "they care as much about style as about issues ? they want Democrats to denounce Republicans loudly and stridently, and to block the administration?s agenda whenever possible." The netroots would not tolerate Congressman Smith adopting a free-trade position -- because that means cooperating with the Republicans. Indeed, since cooperation with the other party is more politically visible than one's ideological profile, this will matter a lot more. The point is, I don't see the netroots generating more free-trade Democrats in the rust belt.