This prediction is much much much too early: Joe Biden, the weakest Democratic candidate for president in modern history -- until Kamala Harris -- beat Donald Trump in 2020 by simply promising a return to something like normalcy. (He of course didn't deliver that, but that's not the point. The point is he won with that message.)
In 2028, Dems will (or at least should) try to nominate someone who can pretend to be normal. Someone from the Midwest, perhaps. Yes, the left will want someone more like AOC and they could get that done but if they choose someone with even a slightly plausible claim to be the "bridge to normalcy" that Biden promised, that person will beat the Republican nominee, esp if the Republican is JD Vance or anyone else who espouses strong admiration for Trump. (Can Gavin Newsom transform himself into a candidate whom independents would support? I don’t think so but he sure is trying hard.)
So then the question is: which party will insist on picking one of their hard-core fringe-base favorite rabble-rousers and which will move ever so slightly toward what moderates and independents want, which is basically to be able to take a breath without wondering what president-caused disaster or scandal or violation of law is about to fall on our heads next.
Ross, many of us hope (likely in vain) for a candidate whose platform represents a shift from radical right or radical left toward common sense, and from whom we can expect civility and maturity. Unfortunately, for such a candidate to have a chance, a substantial part of the American electorate would need overcome its addiction to hyperpartisanship and vitriol. Maybe that’s too much to ask.