> OR use borrowing (e.g. current account deficit). If government spending drives productivity growth then it’s a net positive?

That's basically what already happens. The US has been running a huge deficit for a while now.

It also requires government spending to be the spending that drives productivity growth, which most of it isn't.

> OR tax wealth. If most return on international capital investment is being stored in the US, taxing this effectively taxes profits on international sales???

Why would they store the wealth in the US if the US had a wealth tax? One of the biggest problems with a wealth tax is that it has such a strong propensity to induce capital flight.

It's also not just a question of how you structure the tax. Wealth taxes are hard to avoid for things like real estate (can't move it), easy to avoid for things like factories or intellectual property (can easily move it), but the same is true for other taxes that apply to those things. It's easy to impose an income tax on rental income, so you don't need a wealth tax for that. The hard thing is how to impose any tax on all the money the Saudis have without causing them to just invest it in something else, possibly in some other jurisdiction.