(Sadly, sanity of the opposite political party was / is also highly questionable.)
The problem is systemic: The US doesn't have a functioning democracy. FPTP, gerrymandering, unchecked campaign financing, the electoral college? It just isn't working, and the US is permanently stuck in a dysfunctional two-party system. If that doesn't get fixed (and let's be honest, it won't), the rest of the world won't be trusting the US until it can demonstrate a few decades of continuous trustworthy leadership after Trump is gone.
Quite apart from any sovereignty arguments, cash spent at home goes to purchase of hopefully local components, materials, all along paying for local salaries, which drives local economies. And this is taxed along the way too, as income tax, VAT and ultimate corporate tax.
I wonder if that's really true to a significant amount, and if so, how much does that matter. Eg if I can buy something for X abroad, or c*X locally, for what value of c is this overall breakeven?
I am not holding my breath that he will just walk away in 4 years, why would anybody be so naive? He thinks US constitution is an old toilet paper, its mememe. Look at what happened last time he was supposed to go out.
We have to assume that the US cannot be trusted as a military ally for at least the next 4 years. In fact, we have to be open to the possibility that they will be willing to be hostile. Including, but not limited to, extortion tactics. That's the hard baseline here.
We also have to be open to the possibility that the US either won't or can't have a proper election in 2028. And even if there is a proper election, that even a "sensible" president will not repair the damage.
What is already permanent is that Europe will never have the same level of trust in the US ever again. Perhaps some of it can grow back over a few decades, but the former level of trust will not return.
Because that is where most of the money ends up when the US "supports" other countries. The US unloads weapons from its stockpiles (that need to be replaced at some point anyway) and then replenish the US stockpiles. This is both a huge injection of funds into US defense industry, and it takes care of the expensive problem of dealing with old ordnance.
US defense industry is going to be busy restocking the US stockpiles for a while longer.
If revenue were to soften before that, the Trump administration can distract from this reality by pumping more money into the industry short term. This may actually push the problem forward in time to the next president if they can keep pumping in enough money to hide the problem. It looks as if they are doing exactly this.
Of course, a few years down the line the defense industry will be in trouble as "consumer trust" is gone, Europe have ramped up their production and revenues will start to plummet.
