In the piece Chuck cited, Josh Marshall writes that the Socialist Party "split in two in 1972, when the Cold War wing refused to endorse George McGovern's antiwar presidential platform. Liberal academic [Michael] Harrington led the left-wing group's left wing into a splinter that became the Democratic Socialists of America. The right wing, led by teachers' union chief Al Shanker and others, regrouped as the Social Democrats, USA."
That's not exactly right. The 1972 split was between the Social Democrats (who favored Scoop Jackson for president) and the "Debs Caucus," which favored People's Party nominee Benjamin Spock and reformulated itself after the breakup as the Socialist Party USA. Harrington's circle favored McGovern but stuck with the Social Dems a little longer, before splitting to start the group that later became Democratic Socialists of America. All three organizations still exist.
I am such a nerd for knowing this stuff.
Anyway, it's interesting that Chuck would say the Social Dems want "to exert influence, neocon-style, on Democrats." The Social Democrats USA veer close to being the quintessential neoconservative organization, given that the neocons trace their origins to (a) Scoop Jackson Democrats disturbed by McGovernism and (b) ex-Trotskyists disturbed by the New Left. The Jackson connection I've already mentioned; I should only add that the Socialist Party had, since 1960, functioned more as a group within the Democrats than an actual third party. (They endorsed Kennedy, Johnson, and Humphrey for president rather than field candidates of their own.) The Trotskyist connection is Max Shachtman, whose tiny Trot group—the Independent Socialist League—had joined the Socialist Party en masse in 1958. It was Shachtman's crew that eventually became Social Democrats USA.
So is there a difference between the Social Dems and the neocons? Well, the former never dropped their ties to the union movement, retaining a '50s-vintage labor liberalism along with their hawkish foreign policy. Still, their membership roster has included such prominent neocons as Elliott Abrams and Joshua Muravchik, along with folks who lean further left. (I should add that the group is still a part of the Socialist International, though by now that says more about the International than its American affiliate.)
Did I mention that I'm a nerd for knowing all this stuff?