Absolutely-- and part of the debate, although only part, of the split in the AFL-CIO was how to approach political spending. Unions are increasingly demanding concrete support for union organizing drives as a price for union political support and the primary campaigns against conservative Dems like Cuellar in Texas are part of unions demanding more accountability from Dems for support. But it's not insignificant that only 15 Dems voted wrong on CAFTA, a major tightening of discipline around trade issues from the past.
But as you say, the unions are the only serious progressive money out there. Remove it and national politics will careen even more dramatically to the right. And lose a handful of Senate seats and union organizing will be made essentially impossible under the law. You can delude yourself with chest thumping against the Dems, but if nothing else, they are the votes that keep folks like Charlie Norwood from passing laws to ban card check organizing and every other remaining tool for union organizing.
Nathan Newman