Wrong and wrong.
The GP does not have more clout than organized labor, despite the pathetic and continuing decline of the latter force.
Behind that, organized labor has a _very high_ ability to tell its rank-and-file how to vote. In fact, beyond its "service" support of the arcane mechanics of collective bargaining and labor grievances, the AFL-CIO is now hardly more than a subsidiary of the Democratic Party. Mazzocchi's LP was never on the agenda of the AFL-CIO, which is run by history's most successful Stalinist (without the socialism, of course) bureaucracy, and was certainly never endorsed by it in any meaningful way, outside a few renegade member unions.
Meanwhile, I've personally sat through hundreds of hours of disgusting state AFL-CIO Demo handout sessions, and had my mailbox crammed with wave after wave of AFL-CIO "Vote Demo" pleas. This past election cycle, the state interviewed the DP gubernatorial candidate and wound up endorsing (and paying) the man who scored the worst in the interview. Why? "Because he's going to win." Not a month after he took office, the state was mailing out fliers to members worrying about how we teachers and nurses and day care workers were going to deal with the further budget cuts our endorsee was failing to oppose.
I admit to being nearly on the fence about the tactics of voting for Nader or not this time. I'm on the Nader side of the fence, but still have an ear to the other side. Nonetheless, labor is minor because labor leaders and labor law and our ruling class keep it that way. The AFL-CIO could tip over the whole table on the DP on any day it chose. It simply chooses not to, to its own great cost.
In fact, the AFL-CIO ought to be acting just as you describe -- truly withholding its clout from anybody but genuine friends, who are now few and far between. Instead, it's but an addict that can't stop visiting the DP crackhouse, where the John Kerrys of the world lie to it once in while before picking up their cash.