OTL, the Socialist Party of America, founded 1901, generally won about 3% of the popular vote in US presidential elections, with the exception of 1912 when they managed 6%; and while they endorsed the Progressive Party candidate Robert LaFollette in 1924, who got 16.6% of the vote in one of the more successful third party runs in U.S. history, it was not really their candidate, and in subsequent elections they performed more poorly than even their first five.
Which brings me to the challenge -- with no PoDs prior o their founding, how can the Socialist Party candidate for President (actually being of the SPA) win at least 16.6% of the popular vote in one of the contests from 1904-20?
Bonus points if the PoD is McKinkey surviving.