It’s not the first time snowflake has veered from the natural world to the world of slang. In the 1970s snowflake was a disparaging term for a white man or for a black man who was seen as acting white. It was also used as a slang term for cocaine. But before either of those it was used for a time with a very particular political meaning.
In Missouri in the early 1860s, a “Snowflake” was a person who was opposed to the abolition of slavery—the implication of the name being that such people valued white people over black people. The Snowflakes hoped slavery would survive the country’s civil war, and were contrasted with two other groups. The Claybanks (whose name came from the colorless color of the local terrestrial clay) wanted a gradual transition out of slavery for slaves, with eventual freedom accompanied by compensation to slave owners; the Charcoals—who were also called Brown Radicals—wanted immediate emancipation and for black people to be able to enlist in the armed forces.
The available evidence suggests that this particular use of snowflake never moved much beyond the borders of Missouri or the era.
We should start calling Trump supporters snowflakes as a pejorative. Of course they will embrace it for themselves.
Also interesting that it was Fight Club that brought the word back in its modern negative context.