Sawant’s orientation is to build the vanguard party, and from that perspective, her call for Sanders to run as an independent or on a Green ticket with Jill Stein makes good sense since these small third party formations present an excellent opportunity to “accumulate cadre”. Sanders won’t answer the call, of course, but Socialist Alternative hopes to peel away a substantial number of his disappointed supporters when he doesn’t.
In the highly improbable event that Sanders were to team up with Stein, there’s little doubt such a campaign would far surpass the effort by Nader and Camejo in 2004 because of the much changed economic situation and Sanders’ higher national visibility. However we’re still talking about a very small slice of the electorate: the Nader-Camejo campaign only garnered 0.38% of the popular vote. The same fear that made Democrats and independents who admired Nader’s program finally stick with Gore would apply with redoubled force if Trump or Cruz were the Republican nominee.
Going back to the 1948 campaign of Henry Wallace and the Progressive Party, I suspect it can’t be otherwise until a third party demonstrates it is capable of winning elections and implementing working class reforms. The historical experience suggests this process necessarily begins at the local level, where the odds are better, as the successful campaigns by Sawant and the SA in Seattle demonstrated.
It’s entirely possible, of course, that the dissatisfaction with the two established parties runs so deep at this juncture that a third party bid, with or without Sanders, could attract enough support to become a permanent fixture on the national landscape and begin to effectively compete for office at all levels of the political system. Call this hedging my bet if you like.
See: http://www.counterpunch.org/2016/04/21/the-undemocratic-primary-why-we-need-a-new-party-of-the-99/