Like Trump, FDR had great populist appeal (yes, I know, that hurts). He was able to go straight to the public and browbeat Congress with populism. For progressivism to succeed we may need a leader or at least a figurehead with that level of courage and commitment.
Interestingly, alt-right isn’t especially united. Some are hispanic and some are white supremacists. Some are religiously oriented and some are not. Could be we put too much emphasis on reaching agreement? Sanders galvanized a movement around a few simple “targets”, where targets can be either positive or negative aspirations…