Almost immediately after the ascent of the Left Wing Section of the Socialist Party to a controlling majority of the party's National Executive Committee in 1919, the dynamic of internal party factionalism transformed from the previous battle between the social democratic "Old Regulars" and the radical "Left Wing" to an ideological fight over what to do about the revolution in France.

While Marxist theoreticians within the party like Louis C. Fraina had been left in deep melancholy by the assassination of Lenin, many Communist hardliners remained powerful. They naturally clustered around NEC member C.E. Reuthenberg, who led the more English speaking and Americanized wing of the party's Bolshevik set. Reuthenberg, emboldened by the active role the French Jacobins had taken in their Civil War, was a relentless critic of the CGT's "weakness" and accused Syndicalists and Anarchists of being pseudo-reactionaries in league with the Kaiser.

These outrageous claims from revolutionary vanguardists so recently discredited by the failing trajectory of the Russian Revolution had unleashed the raging fires of Syndicalism that had long burned within the party, which had maintained many members of the Industrial Workers of the World despite anti-sabotage clauses in the party constitution meant to keep adherents of that revolutionary trade union out. John Reed's youthful sidekick on the NEC, Benjamin Gitlow, was the strongest proponent of supporting the CGT trade union and their leading role on the revolutionary side in France. While they were weak on the Executive Committee, the Syndicalists represented many of the party's most active labor organizers, such as William Z. Foster who at the time of the party's infighting was supporting a massive strike in the steel industry. Foster, who had visited France and studied the CGT in 1912, had been an early supporter of Syndicalism. His young associates such as Earl Browder and James P. Cannon would, over time, become leading lights in the Syndicalist faction of the party.

With the old leadership of the Left Wing dominated by Communists but the young guard strongly in the Syndicalist camp, it was up to the Left Wing's newly minted Executive Secretary of the Socialist Party, Alfred Wagenknecht to chart a middle course. On the NEC his footsoldier was his fellow German-American, L.E. Katterfeld, a man known more for zealous commitment than wit or stratagem. This new Center faction, an awkward position for radical Leftists, naturally accumulated the surviving members of the Socialist Party's Old Regulars and rest of the former party Right. In their astonishing speeches at the Emergency Convention that year, John Reed and the party's longtime Chairman the esteemed Eugene V. Debs clearly made the case for the Center and for reconciliation between not just the Communist and Syndicalists, but between the Socialist Party and the IWW.

The accomodation within the Party did not last for long, however. By 1923 Reed's experience in the short-lived Seattle Commune had turned him into a full-throated Syndicalist and by the British Revolution in '25 it was clear which side was on the ascent not only in the Party but among the Left worldwide. The death of Debs in 1926 left a hole in the party that was not easily filled. His natural successor, party historian and theorist Morris Hilquit, was a member of the old Right wing. His tenure was shortlived and chaotic but did make the way for his pupil and manager of his successful Congressional campaign in New York, a Christian Socialist named Norman Thomas.

At the very time int he late Twenties when the Party was winning seats in the Representatives and Senate in the Midwest and New York, Thomas brought with him an injection of radical dissidents from mainstream America. These were radical and passionate people, often not Marxists of any stripe, that became known as the Liberal faction of the party; not for social democratic inclinations but due to their mixbag variety of beliefs and generally pacifistic and evangelizing nature. By '28 Thomas had risen from obscurity to being the Party's presidential candidate, less important than the Executive Secretary or the Chairman as they had not yet adapted to the realities of being a truly mass movement with real electoral chances. On the same wave that brought Thomas to be Mayor of New York City, John Reed became the Junior Senator from New York. This was the moment that the battle lines for the future of the party were set.

With the Communists at that point under the leadership of J.B. Salutsky faltering from lack of new blood, the Liberals were the most vigorous opposition to Syndicalist orthodoxy in the Socialist Party of the 1930's. Reed meanwhile became increasingly social democratic during his time in the Senate, and had his eyes on a Presidential run himself. He cultivated the Center, which had seen the old social democrats gradually replaced by slightly more militant but still solidly practical Sewer Socialists from the Midwest, led by Milwaukee mayor Daniel Hoan. The Syndicalists weren't unified in their attacks on the unorthodoxy of the Liberal carpetbaggers in the Party, however. As time went on Foster and his state socialist view of French-style Syndicalism was chafing against proponents of English style trade union democracy.

By 1936 the Socialists had finally adapted from a party in theory to one in practice, with political candidacies being finally seen as more valuable than internal chairmanship positions. In that way the primary election within the party to select its presidential candidate was a chance to seize not leadership of the party as well as an increasingly good chance at the highest office in the land. Nominated by Browder and his other supporters, trade unionist and Syndicalist theoretician William Z. Foster was put forward by the hardest edge of the Syndicalist faction, splitting them.

Other trade union leaders, Syndicalist by the example of the British TUC rather than a revolutionary political education, rallied around former muckracking labor journalist and activist turned Socialist Senator from California, Upton Sinclair. Despite some comparisons to the Liberal faction, Sinclair had deep routes as an organizer and supporter of the labor movement and had friends all throughout the CSA labor conference. Most notably he was the candidate preferred by powerful West Coast union leader Harry Bridges. Bridges, the man who had led the strike that organized the dockworkers and sailors of the West Coast and American Pacific into a single powerful union, was unable to run himself as an Australasian immigrant.

Senator Reed found himself with the confidence of most of the Socialist delegation in both Houses of Congress, as well as many of the Socialist mayors and governors of the Midwest through his alliance with the Sewer Socialist movement and his apt leadership of their caucus in navigating the waters of the Democrats and Republicans. Draft legislation promised a potentially revolutionary reworking of American capitalism within the context of state-run social programs and other institutional reforms from within the system.

And of course, once again, Norman Thomas was intent to run for the presidency. Even without much of the support of the Combined Syndicate movement of labor, Thomas had been the face of the party as it had spread to mainstream acceptance among left-leaning members of the American middleclass. In small town America he was the difference between the Socialists being viewed as frightening foreign Syndicalists or as All-American friends of the common man.

One example of how the primary was dividing the party was the way it split the leaders of the Party subsidiary Negro Labor Congress. Alumni of the underground revolutionary African Blood Brotherhood such as Cyrill Briggs and Harry Haywood supported Foster, with a vision of black liberation in America through centralized socialism. Trade union leaders like A. Philip Randolph, who had organized the traditionally black Brotherhood of Sleeping Car Porters in the Twenties, were naturally more inclined to the English Syndicalism of Sen. Sinclair.