Eric Garcetti started the climate mayors initiative, secured a bid for the 2028 Olympics, and he will likely win the Senatorial race in California next year. He's going to have a ton of momentum going into 2020. He will easily steal Booker's lunch.
California's recreational market should be booming by then as well, which will force the hands of a lot of states. Consequently, I fully expect national legalization to be part of the party platform in 2020.