They can, yes. The power of the federal government to do that to people is immense. But that is not the same as the Bill of Rights disappearing. The federal government has a ton of power within the law's constraints.

That does not mean that the federal government has now slipped the law's constraints and can (for example) start waterboarding people or seize people's records without complying with the Fourth Amendment. That's the category error. The feds doing terrible things that are allowed by the law is different than them breaking the law. Still bad, but different.

Correct, the Bill of Rights hasn't disappeared entirely. It has disappeared selectively, at the whim of federal agents wantonly arresting or killing people in the streets, or an attorney general who picks out victims based on how much their behavior, or their mere existence, bothers him. Most of us may live as if our rights are protected, until they're not. Even in the worst dictatorships there are still legal systems, and many people are treated lawfully as long as the regime doesn't pick them out for "special treatment". There's also a flip side to violating people's right. Criminals who have been lawfully charged and convicted, are being pardoned, released, and compensated by the regime, because the regime views them as allies. Every time that happens, YOUR constitutional rights are being violated.