In 1926, Upton Sinclair ran for Governor of California as a Socialist, winning 4.02% while Businessman Justus Wardell won 24.69% and Lieutenant Governor C. C. Young, a progressive who primaried the more conservative governor Friend Richardson (a victory of 1.99%), would win the election itself with 71.22% of the vote. He'd (Sinclair) try again as a Socialist in 1930, winning 3.65% of the vote to Democrat Milton Young's 24.13% and Conservative Republican San Francisco Mayor James Rolph, who primaried Young (a victory of 2.16%), who won the election with 72.22%. Rolph would go on to die in 1934 and be replaced by Frank Merriam, his Lieutenant Governor. In that year, Upton Sinclair ran as a Democrat, winning 37.75% to Merriam's 48.87% and Progressive lawyer Raymond A. Haight's 12.99% and it's believed that Merriam could've been beaten of Haight didn't run though I doubt it. Upton would never again run for political office, though he had been the Socialist candidate for CA-10 in 1920, winning 17.3% to incumbent Republican Congressman Henry Z. Osborne's 82.7% and the Socialist candidate in the 1922 Senate Race, winning 6.28% to Incumbent Republican Hiram Johnson's 62.17%, Democrat farmer William J. Pearson's 23.76%, and Prohibition Los Angeles County Supervisor and businessman Henry Clay Needham's 7.79%. In 1934, Sinclair's platform was on the End Poverty In California plan, or EPIC for short, which FDR likely borrowed bits and pieces of for the New Deal.

If Sinclair had been the nominee for the Democrats in 1926 under a EPIC platform, could he have won against Richardson? If so and say FDR loses his 1928 Gov Election like he came close to doing OTL, would Sinclair have been picked for the 1932 Presidential Election, who would be his running mate if he was, what would his cabinet look like and his version of the New Deal, and how would he govern in both domestic and foreign affairs?
Sinclair only has a hope of winning if its in the midst of the great depression and with Roosevelts endorsement, so he cant ever get elected in 26, and he couldnt run against Roosevelt and knowing him I dont think he would. Sinclair really deeply respected the guy. Maybe you could say Roosevelt is assassinated after or even because he endorses Sinclair and then Sinclair sweeps to the democratic nomination in 36. Foreign policy wise, he was a real internationalist so i think we'd be in good hands there. Domestic policy wise he was kinda a kook and his ideas werent really accepted even in mainstream socialist circles so i wouldnt be confident in them working out too well.
Sinclair's End Poverty in California (EPIC) program called for the seizure of idle factories and farms and to take unemployed members of society, train them in the fields, and then hire them to work at those factories and farms. It was an incredibly important precursor to the New Deal, but I'm not sure an End Poverty in America (EPIA?) movement would go over quite as well --- especially with the Red Scare in living memory and a self-declared socialist in the White House (although the CPUSA and USSR hated him).

Oh, also. Despite what some may claim and did claim, Sinclair was not a communist. I'd hesitate to even call him a Marxist --- he definitely didn't fit the bill of a socialist in Marxist terms. He was no friend of the CPUSA nor CPSU and gave a pretty harsh beatdown to communism in 1930. Sinclair, in my opinion, can be best described as a utopian socialist --- his ultimate vision was for workers in industries to vote to create a socialist society and the ruling class must accept that vote. You're not going to see the USA ally or even be friendly with the USSR until around the same time OTL, assuming he runs for a second term in 1940.