If it wasn't for reddit supporting /r/TheDonald, there is a good chance MAGA might not have ever happened, at least not in the way it manifested.
Trump was able to get a significance amount of grassroots support early on, and it almost all came from /r/TheDonald. This was before anything was really happening on other social media. People that were disenfranchised with Obama pretty much went with either Bernie or Trump. It was a warzone on Reddit. Both Bernie and Trump did AMA's and this blew them up popularity wise.
What Bernie didn't have that Trump did was an army of russian bots supporting him.