I think something similar happened in NY. Trump got 23% of the NYC vote, a gain of nearly 6% from 2016. But he lost a lot in the Long Island / Westchester suburbs + Upstate.
In 2016, Trump basically matched Hillary in NY State outside of NYC (67,000 votes for Hillary was the difference between them outside of NYC). In other words, NYC basically gave Hillary her win in NY State.
In 2020, though, NYC gave Biden a 1,630,077 advantage over Trump. Biden won the state by
1,992,889. That means Biden won all of NY, minus NYC, by 362,812 ... a near 300k improvement over Hillary outside NYC
If Trump hypothetically had matched Biden outside NYC (just as he had matched Hillary in 2016) and held on to his urban gains, he would've hit 42% in NY State (versus about 55-56% for Biden). A 42% performance in NY State lines up with a 45-47% performance in NJ
It makes sense. My question is, why did he improve in the urban cores vis a vis 2016?
Because that's where Minorities live.
And in the long process of switcheroo: Democrats gain the Upper Class White vote, while Republicans gain the Minority one.
Voters start to assort themselves along class lines, rather than race, a return to pre-1960's style but Republicans and Democrats switch places.
But it's a very long process that will last at least another decade to complete, maybe two.