What’s missing from your analysis is the material backing of the parties. The Democrats and Republicans, with the backing of their corporate donors, both represent the interests of the capitalist class. They have their differences in some areas, but neither is interested in disrupting the fundamental relationship between classes and the means of production, which is what grants capitalists their power. So winning or losing elections is less important to them than winning while compromising on that core class interest.

One could choose to reverse your reasoning to say that the Republicans are free to become more and more progressive without being punished

Two things: Why would they? If they want to serve capitalists and they can get away with doing so, they’re gonna do it. Second, in a superficial rhetorical way, they have made appeals to progressives. They use some of the language of economic populism talking about elites controlling you, or the economy giving you a hard time, corporate censorship of media, failures of institutions, and the way we spend money on awful foreign adventurism instead of on helping people at home.

Of course this is all for show and for the things they don’t just straight up lie about, they subtly twist the messaging to play to the same feelings while turning the attention to things that aren’t the problem. Failings of institutions becomes anti-intellectualism. Economic worries get directed to competition with immigrants and foreigners instead of the capitalists exploiting all of them. Corporate censorship gets turned away from the influence corporations have over our communications to just being about crazy woke people who “don’t understand how things work” and can’t handle people “telling it like it is.” Isolationist isn’t about being anti-war or anti-multinational corporations, it’s about how wars don’t benefit Americans enough and how outside influences from scary foreigners is corrupting the country.

Post Clinton and Obama, the Democrats became the party of “everything is fine except for those dumb dumb bigots.” And after Bush, the Republicans pivoted to the counter-narrative of that while still maintaining their priority towards the interests of the capitalist class. So neither party is really addressing your concerns, but one seems to be at least acknowledging the problems you have and telling you you’re a super special person and the other party seems to be ignoring your pain and kicking you while you’re down.

And of course with Republicans in power, I’d expect these roles to flip again. Once Trump does enough of his bullshit he’s gonna say everything is great except for those whinny wokes and the Democrats are playing opposition to that, even against policies they supported while in power like deportation, but only go so far as saying that things were better before Trump ruined everything. If we could just go back to before that everything would be fine. Even more specifically, post Trump there has been an effort to pin things all on specific people rather than any structural critique or even going to far as to broaden it to the party as a whole. “There are good, honest Republicans I might disagree with, but respect, but Trump is pure evil and everything bad that’s happening is specifically because of him” or some other rotating cast of figureheads like Musk, Desantis, etc. even though all of these policies are things Republicans have been working towards for decades, sometimes with the help of Democrats.

So no, I don’t think the stances of the political parties ever really ebbs left based on who wins elections. We had 8 years of “Hope and Change” Obama and the party completely balked at Bernie for actually wanting to follow through on the empty rhetoric of Obama.