The problem is that there's no realistic way to fly across the US, supersonically, without massively impacting a substantial fraction of the electorate (who will enthusiastically vote for anyone who will stop the noise).

You can read about the supersonic experiments over Oaklahoma City in the 1960's to learn about the effects of sonic booms, and why people don't like them.

For reference, the Space Shuttle generated annoying sonic booms over west Los Angeles when landing at Edwards Airforce Base. The approach path to Edwards is more than 30 miles from west LA. So, for any supersonic airway, you'd need to set aside a roughly 60-70 mile wide swath of land. That's a lot of people voting to shut down your SST operation (or suing you).

Sure, but I don't see a startup called Boom changing the political landscape around sonic boom concerns, particularly not in an era where there's also a lot of environmental lobbying.

if they revive the noise implications they might well manage to change it. IMO those restrictions are also because it wasn't an American jet so it kept the competition out.

Agreed on both points, but they're fighting against the physics of sonic booms, not just Concorde's noisy turbojet [a solved problem] so I wouldn't bank on it, and lobbying against Boeing as well as an environmental lobby that's far more influential now than in the seventies.

Several European states without commercial airframers introduced supersonic overflight bans too and the Anti Concorde Project started in the UK so I don't think the argument it was all protectionism stands up anyway.

I think this issue was range. Many of the over ocean routes it simply couldn't fly. One of the reason BOOM believes in themselves is that they open up many more routes.

Boom's planned range of 4,500 nm is actually only a marginal improvement on Concorde's 3,900. Their site advertises routes like "LA-Sydney", but at ~6,500 nm this won't work without a refueling stop.