In the US labor unions can support candidates of their choice in elections.  That support can be an important part of the "ground game" come election time and is going to be much more pronounced for a candidate who supports labor issues.  An increase in the number of union members can make disregarding the interests of labor more difficult for Democrats in general.  But for this to be true Democratic elected officials and union leaders will need to learn better ways of communicating with union members and of addressing their concerns so the Republicans cannot siphon them off on bogus "social wedge issues."

Outside of the big cities, organized labor is pretty worthless as far as the ground game goes.  They organize about as well as GM sells cars (as Howard Dean, John Edwards, Dick Gephardt, and Hillary Clinton have all discovered).  The college kids running the Obama campaign did better than I've ever seen the unions do.

Union endorsements also carry very little weight with actual members, because union members do what they want at the polls.  It's not a sufficiently solid bloc to warrant any great amount of attention.  Kerry took about 60% of union members.  Obama took about the same.  They deliver endorsements, but they can't deliver the votes.  The return on investments in new and sporadic voters are much higher than on the unions.

Which isn't to say we shouldn't support unions and their efforts to expand.  We should, because it's the right thing to do.  But let's not suffer the illusion that the unions are really getting us anything electorally.

Conservatives want live babies so they can raise them to be dead soldiers. - George Carlin