Some progressive ideals are what the average American wants. Many are still very hard sells. What the Dems need to realize is that the political-junkie conceptions of 'centrist' and 'progressive' mean very little to the 'swing voters' they're trying to appeal to. They don't want a coherent ideological approach. Not that that seems to stop 'centrist' Dem reps from constantly trying to chase policy rightwards.
Demilitarizing the border and legalizing most of our immigrants?
These two are in opposition to each other. Selling the public on amnesty for whoever is here already requires a credible plan to prevent more illegal entry.
Broadly speaking, higher taxes required to responsibly fund progressive programs.
You have to convince folks they'll get their money's worth.
Particularly rural areas are skeptical, they think they get money taken from them to solve city problems, and even if they might be able to benefit, the program might not be able to reach them.
So you might have decent luck with medicare for all (though there's a huge special interest influencing them against that too), but if you wanted big infrastructure and transit plans, they'll think the government is going to toss money at the cities and do nothing for them. Or worse, they'll be one of the folks that get eminent domained to bulldoze their home to make way for rail connecting two big cities.