Norman Thomas and his radical pacifist co-thinkers and their young Marxist allies of the Militant faction sought to build a mass political movement by transforming the Socialist Party into what they called an "all-inclusive party." Not only would an appeal be made to the radical intellectuals and trade unionists who were the historic core of the organization, but an effort would be made to work closely with the Communist Party in joint actions, and to infuse the Socialist Party with the leading personnel of small radical oppositional organizations, including in particular the anti-Stalinist communist groupings headed by Jay Lovestone (the so-called "Lovestoneites") and James P. Cannon (the so-called "Trotskyists"). To be sure, an impressive array of left wing intellectuals came into the Socialist orbit as a result of this venture, including (from the Lovestoneites) Bertram D. Wolfe, Herbert Zam, and Benjamin Gitlow; as well as (from the Trotskyists) Max Shachtman, James Burnham, Martin Abern, and Hal Draper. A broad array of radicals from other tendencies also contributed to the pages of the party's official theoretical journal, including from the Communist Party orbit Joseph P. Lash of the American Student Union, the radical novelist James T. Farrell, public intellectual Sidney Hook, leading American Marxist of the 1910s Louis B. Boudin, and Canadian Trotskyist Maurice Spector, among others.
A very real bid was made to unite the factionalized and marginalized American Left in a common cause — and great hope was held for success in the enterprise. After the rise of the Nazis in Germany and Austria by 1934, no longer did the Communist Party engage in its Third Period epithets against the Socialists as so-called "social fascists". Lillian Symes wrote in the SP's theoretical magazine in February 1937 of the "incredible change" seen to be taking place in the Communist Party in its seeming abandonment of sectarianism and move towards building a broad "people's front" against fascism. At the same time, other radical organizations sought to alter their tactics so as to rapidly build and aggressive left wing organization to stand in opposition to nascent fascism. From early 1934 the French Trotskyist organization had entered the French Socialist Party in an effort to build its strength and win support for its ideas. Pressure to follow this policy of the "French Turn" was building among the American Trotskyist group. For a brief historical moment in 1935 and 1936 the vision of the SP as an "all-inclusive party" which aggregated radical oppositionists and possibly even worked with the Communist Party in common cause seemed achievable.
In January 1936, just as the National Executive Committee of the Socialist Party was expelling the Old Guard, a factional battle was being won in the Trotskyist Workers Party of the United States to join the SP, when a national branch referendum voted unanimously for entry. Negotiations commenced between the Workers Party and Socialist leaderships, with the decision ultimately made to allow admissions only on the basis of individual applications for membership rather than en masse admission of the entire group. On June 6, 1936, the Workers Party's weekly newspaper, The New Militant, published its last issue and announced "Workers Party Calls All Revolutionary Workers to Join Socialist Party." Approximately half of the Workers Party heeded the call and entered the SPA.
Although party leader Jim Cannon later hinted that the entry of the Trotskyists into the Socialist Party had been a contrived tactic aimed at stealing "confused young Left Socialists" for his own organization, it seems that at its inception, the entryist tactic was made in good faith. Historian Constance Myers notes that while "initial prognoses for the union of Trotskyists and Socialists were favorable," it was only later when "constant and protracted contact caused differences to surface." The Trotskyists retained a common orientation with the radicalized SP in their opposition to the European war, their preference for industrial unionism and the CIO over the trade unionism of the American Federation of Labor, a commitment to trade union activism, the defense of the Soviet Union as the first workers' state while at the same time maintaining an antipathy toward the Stalin regime, and in their general aims in the 1936 election.
Norman Thomas attracted nearly 188,000 votes in his 1936 Socialist Party run for President but performed poorly in historic strongholds of the party. Moreover, the party's membership had begun to decline. The organization was deeply factionalized, with the Militant faction split into right ("Altmanite"), center ("Clarity") and left ("Appeal") factions, in addition to the radical pacifists around Norman Thomas and the midwestern "constructive" socialists around Dan Hoan. A special convention was planned for the last week of March 1937 to set the party's future policy, initially intended as an unprecedented "secret" gathering.