One of the things I find really interesting as a Brit is hard to put into words:

Americans tell us that we don't have a constitution — when we do, it is just not wholly written down. (It is in part).

We have a constitution that is flexible and precedent-based, but pretty stable, and it has emerged on top of the bits that are written down, and has amended them over time (for example, it is built in part on Magna Carta, but only two or three of its principles remain in law.) Notably a bit more of it got written when we agreed to be bound by the ECHR, but that was mostly absorbed into our understanding.

It has taken us hundreds of years to get to this stability, and it is defended from attack from pretty much all sides; every government risks changing it and there is pushback each time, because you can't govern if there aren't rules. The rules are precedent and convention, and there are various authorities and archives that are consulted to work out what they are if people think they are at risk.

We are regularly told by Americans that this is an intolerable thing; we need a written constitution or we can't know what our rights are!

But those same Americans, right now, are engaged in exactly this process. You have a set of written rules that give Congress power over things, and you are currently evolving a set of precedents that suggest that the executive can simply wander past them and Congress somehow shows deference or refuses to assert its power in some situations.

You're right at the start of building an uncodified constitution on top of the old one just as we did on top of Magna Carta.

It's not entirely new to Trump; every President in my lifetime has pushed on this except maybe Carter. And sometimes they push back (Roe v. Wade was part of this uncodified constitution and probably needed to be a written amendment.)

It could work out but it's important to understand that is what you're doing. And it's not just Unitary Executive theory or presidential immunity; the emergence of the Supreme Court's "shadow docket" is emblematic of the same process.