The vast majority of members of each party are the same people. But, there is a significant portion of the Paul Ryan party (upwardly mobile) that does not like Donald Trump very much at all. There is a significant portion of the Trump party (in rural areas, in the Rust Belt states, among some Hispanics and blacks) that doesn’t quite hate the Paul Ryan party, but is rarely excited enough to vote by the Paul Ryan party alone.
In 2016, the prospect of Hillary Clinton made for a nearly unanimous and unified front of the Paul Ryan party and the Donald Trump party.
In 2018, the Paul Ryan party ran for their House seats, having passed a Paul Ryan tax cut, and they got wiped out.
In 2020, most of the Paul Ryan party came out to vote in their House and Senate races. They performed much better, because they were joined by almost the entirety of the Trump party voters. Donald Trump was on top of the ballot, and those Trump party guys who aren’t members of the Paul Ryan party shrugged and voted for the Paul Ryan party guys down their ballot.