Referring to the ISO as large is a sign of the shrunken horizons of the U.S. far left. Compare the thousand or so members they now claim--and as an ex-ISOer I'm always especially skeptical of their membership figures--with the CP back in its day. Not even the nearly hundred thousand of the Popular Front period, when they were going with the New Deal tide, but the early membership of tens of thousands when the party first got together, under conditions of illegality. And that was when the country had less than half the population that it does today. To have an impact on the national political scene, to be a revolutionary vanguard party, an organization would need tens of thousands of active members, many of them positioned in key locations and industries. I don't think any currently existing organization, no matter how large compared to its smaller brethren, is going to get there through a linear process of individual recruitment. Which of course does not negate the necessity of building such organizations based on where one finds programmatic agreement, but requires recognizing that between now and then some qualitative changes will be necessary.