100%

The reason there is no unringing this bell is not just that we have a capricious, vainglorious president, it's that all of checks and balances that are supposed to restrain the executive have proven worthless so far. Republicans in Congress have completely declared their impotence, having fully relinquished their duties that the Constitution specifically delegates to the legislative branch, like tariff power, war powers, etc.

A terrible potential is that US products may find themselves unable to get footing internationally, due to broken trust and increased competition, so instead they'll try to rely on every-expanding protectionism and corruption to stay dominant in the US market.

Just as we've seen in the car industry we'll wind up less innovative, less productive, and less economical.

Absolutely not. History has shown again and again that human memory is short and greed is unbounded. If there isn't an active fire burning under people's asses they'll choose the $0.01 cheaper option even if it ends up being much worse for them in the long run.

That, plus massive influence campaigns from Russia, China, and US oligarchs like Musk and Thiel, are how we came to be living through the current general disaster.

There's no memory to be needed. The US is officially an unreliable ally. They have been for several decades now. They will continue to be so. EU politicians might've been overly ambitious but they're not naive.

Exactly. Trump is just the messenger. The underlying problem, festering for decades, is that a large enough fraction of the US population thought that Trump was even remotely qualified to lead a country to begin with.

The fact that we didn’t immediately remove him after the Greenland letter just demonstrated to our allies that that same fraction of people also don’t value our relationship with Europe.

The CCP looks thoughtful and stable by comparison. It’s too bad that the result of this will be to force more people to align with them, because they’re just as self-serving as Trump, they just have the good sense and temperament to hide their true intentions.

The fact that we didn't jail/banish him after leading an insurrection against the US Capitol was the "too far gone" moment.

Anything after that, is just Yet Another millimeter along the same trajectory:

Well, if we let him get away with J6, then I don't see how this is too much worse.

To tie this to your point, I honestly don't see why the Greenland letter should suddenly be the straw that shatters this particular dromedary's spine.