Now is the perfect opportunity for the left. Remind people that the Democrats won't protect them from people like Trump. Organise and strengthen your community. Give people hope.
The realization that theres a non insignificant amount of Americans who hate the status quo but didn't vote for Trump is actually a good wake up call. Its going to be an absolute uphill battle, but leftism actually has a chance of having an actual movement in America.
Im gonna see if theres any orgs I can join near me, and I hope that everyone else can too.
Joining an existing org is most likely for the best, but also consider rolling your own. You can do both, ofc (just campaign within your miniparty to disband and convert to the larger org you're working with at some point).