Trump is "popular"...
...for very small values of "popular".
He is popular with some elements of the Republican Party. Democrats (and many career Republican Party members) can't stand the man, but I can't deny he has a gift for self promotion and wearing invisible clothes.
The problem with the US Constitution and Bill of Rights is that they're treated as holy gospel, rather than some opinions of some slave-owning landowners. (Sometimes, I wonder just how many US citizens actually understand the meaning of the word "amendment". The v1.0 release didn't even include that oft-quoted* "right to bear arms" bit.)
It's also worth nothing that another country rather closer to the UK effectively copied and pasted it into their own constitution. That country is Switzerland. If you ever wanted to know what the men who drafted that document actually intended, I suggest taking a closer look at the Swiss political system.
As for the obstructionism: this is inherent in the nature of the legal system in use. The US inherited the UK's Statute Law system, which starts from the principle that everything is legal unless a law decrees otherwise. Banning something therefore requires adding new laws, increasing the number of laws on those statute books and making life just that little bit more complicated for the legal profession.
By contrast, most continental European nations use the Roman (a.k.a. "Napoleonic") System, which takes the opposite starting point: all things are illegal unless a law states otherwise. Thus banning something in France or Spain merely requires deleting the laws that allow it. Unlike the UK and US, this tends to make the nation's body of laws smaller.
(This is one of the less-publicised problems with the UK has had with the EU: Most EU members use the Roman System, so simplifying their laws makes sense. This means EU Directives tend towards banning things as, for most member states, that means removing laws from their books, not adding to them. But the UK has to add reams and reams of pages to its groaning statute books every single year to keep up with these changes. The two systems are fundamentally incompatible.)
In both systems, there are often unexpected consequences and corner cases that complicate matters, which is why good lawyers get paid so much. In the UK and US, laws are refined over time by judicial precedent: a judge makes a decision in a case and, if that decision sets a legal precedent, it is effectively treated as part of the related laws and used to decide similar cases in future. (As the UK and US legal systems are so closely related, it's not unusual for a judgement made in the UK to also be used as a precedent when deciding similar cases in the US.)
The upshot of all this is that Statute Law systems tend towards bloat. As legal systems are the closest things our societies have to an operating system, this is not a good thing. Even lawyers agree on this. (The relevant bit is towards the end. It's a fascinating programme.)