What does the post-Trump GOP look like?

[Kamala's side hoe]

Interesting food for thought from Re: Will generational turnover favor Republicans this time?
Shifts in relative partisanship could drive changes in the parties' platforms.

Yes, but 2024 is likely too soon.  As others have noted, this really kicks in when a lot of people born after the 2008 crash become eligible to vote.  There are 2 components to this:

1. Statistically, post-2008 children were very disproportionately born and/or raised in the South.  Between fewer pandemic school closures and abortion restrictions, this is likely to get even more dramatic for post-2018 children. Regardless of whether national politics shifts Republican, what's more clear is that culturally Southern influence will grow.  This also means the South will come to functionally control K-12 education.  The 2030 census could be an important turning point for this as by most models the South cumulatively gains a medium size state worth of EVs.  There is a world in which this greatly benefits Republicans.  However, it's also possible that Democrats will gradually become more effective at competing in the South as we have seen in GA and VA over the last decade or so.  

2. Certain non-Southern megacities are approaching a new equilibrium in which only devoutly religious people get married and have kids in significant numbers.  This could be driving the R trend in NYC and parts of CA.  Given the astronomical Dem margins in these cities most likely it will be a slow generational climb out of the basement, like when R's gradually broke the Solid South after WWII.  However, if NY becomes a competitive state from this, it would be a political earthquake.

3. If the economy falters meaningfully in the late 2020's/early 2030's, there will be a forced choice between cutting social security and medicare or raising taxes significantly on young people to keep it stable.  Democrats seem likely to choose the latter, which could alienate young families.  Parents in particular may be less concerned about old age benefits because they could rely on their children to some degree if necessary.  

Put these together and my main takeaway is that today's Democrats have become unsustainably socially liberal for the long run.  However, there's also a considerable risk to R's from Trumpy populism if it alienates enough of the South over time.  

To be fair, even pre-2008, the idea of raising multiple children in a large family was always more associated with Conservative politics. If you look at where people were raising Children in say the 70s, 80s, or 90s, it was largely Republican-leaning suburban communities, and that hasn't panned out in Millennials, even white Millennials being notably more Conservative - quite the opposite infact. I would also point out as you concede that the South isn't a universally Republican/Conservative region; where within the South people are having kids matters a ton here.

I also think an important missing variable is how strongly offspring are influenced by their parent's politics. If it's only a relatively modest or weak correlation, other factors like different cultural circumstances for the new generation could easily overpower any bias caused by parental politics. What would scare me the most as a Dem would be if the people having the most kids are all the hyper-religious homeschool types that raise their kid in a very small bubble, cause that gives parents a ton of ability over their kids worldview and belief structure, but I think that still is a loud minority.

I'd also add for #3, presumably Republicans would have to take up the opposite position of cutting or eliminating SS and Medicare, which would still be unpopular with young people, especially people around the ages of 25-35 who have already paid into SS for a few years feeling like they're blatantly being robbed. This is still a complete hypothetical though so it's truly impossible to say what would happen.

Well, as I acknowledged, more culturally Southern doesn't necessarily have to play out as more Republican.  It probably starts out that way on the margins with the parties competing on the current issue sets, but it doesn't have to stay that way. In the highest fertility Southern states (basically Texas and everything bordering it), plenty of moderate "normies" are still having 3 or 4 kids.

The potential for a more dramatic shift is where it's only the social conservatives having kids or having a 2nd kid.  However, they are also starting from only ~20% of the population in those places.  On a related note, it will be interesting to see if a religious group that renounces contraception ever gains serious political power in South Korea or Japan.  That could be a harbinger for whether this type of dramatic change would viable in the lowest fertility NE/West Coast states.

Regarding the social security stuff, I think a lot of young people have already written it off and/or assume they will get less than half of what was promised.  Add in families where either the parents are getting more support from the children and/or the children will be inheriting more than social security could ever provide, and I think a lot of young families would prefer social security cuts to tax hikes.  Keep in mind that a lot of affluent large families have used the stratospheric Trump era estate tax cutoffs to essentially set up a private welfare state/UBI for their descendants.

This is all medium/long run stuff, though.  In the short run, I am more upbeat than CW for the Dems.  Unemployment should stay structurally low as long as the Baby Boomers are old enough to be retired and young enough to do a lot of (non-healthcare) consuming and the accumulated effect of the 2020 census maps means 2028 is their best chance of a significant EC advantage compared to the popular vote in a long time.   IMO both parties are facing short term and long term incentives that are reversed, because of the likelihood that the South replaces the Midwest as the pivotal region in presidential elections.

I'm curious where in CA there's evidence of R shifts from fertility differentials. I understand the mechanism behind this happening but haven't seen anyone post spatial data indicating that this is happening. All I've seen recently are vague claims that highly educated parts of the Bay Area have shifted mildly R despite increasing educational polarization, which I suspect mainly have to do with increased turnout in Titanium D (and heavily POC) suburbia.