In the 30's Thomas and the Socialists did do better but most of the left wing/protest/working man vote went to that other socialist in the race FDR.
This is true. It's worth remembering, though, that FDR campaigned on a conservative platform- indeed, he ran against Hoover from the right. It's actually a bit of a mystery why Thomas didn't do better in 1932.
Thomas did alright, right at Debs average higher 2% range, in 1936 with a large pool of voters that would have supported Thomas going to FDR. He was then killed in 40, 44, and 48 because of his anti-war stance and the rise of the Soviet Union.
Also true. Which is unfortunate, because Thomas was a ferocious opponent of the Soviet Union (and he entered the race in 1948 only to provide a leftist alternative to Henry Wallace, whom he thought was being manipulated by the Communist Party).