How would the Socialists take power? I need help with the POD, as that's the main reason why my TLs haven't worked out.
Well the first step is the WWI issue.
The SPA opposed America's entry into it, having viewed it as 'a war between Imperialists' that America, as a country valugin liberty, democracy and equality should have nothing to do with.
Now, by the time it was clear that the Entente was going to win the public had shifted to support, while the SPA continued its position, so either get the American public to continue their oposition to it or have the SPA change their position early on, perhaps under the idea that 'through winning this war we can kill Imperialism and Free the World'.
Another related thing was that that the Congress pased the Espionage and Sedition Acts, which basically (at the time) made it illegal for a group or a politican to question or oppose the war while the United States was involved in it and generally massively limited freedom of speech, so you'd have to find a way around that as well.
Now, if you can find solutions to the above than with the SPA remaining a force in politics, it will inevitably become popular during the Great Depression., even if, as per OTL FDR steals their ideas and implements weakened versions to try and make them less popular.