Popularity is the core of everything in a democracy. The reason Republicans are terrified of Trump and fall in lockstep is that Trump can get rid of them via primaries, and that requires Trump's popularity with a small but rabid MAGA base. But Republicans in 2028 will have to survive an election without Trump bringing that base to the ballot.

If Trump's popularity falls to Nixon levels, and the MAGA coalition continues to fracture at the current rate it's falling apart, within a year or tow, there could very well be 60 votes in the senate that go against Trump.

That is probably when he leaves office - but congress can stop a lot of things he is doing if they try.