Owning a business in a country where the taxes are lower than the US corporate rate triggers double tax, as well as any passive income investments. The US can tax a residence that sells for a profit while the residential country will not. Disability support earners have been taxed on their income from their resident country as well.

I have no idea why you might be downvoted, but it's extremely unlikely you'll end up owing more than 100%.

I'm not an accountant but having filed multi-jurisdiction tax returns myself I don't see a mechanism by which this could happen.

I edited my comment, since 70% tax rate is actually possible depending on the tax rate of the country you're living and whether they have a tax treaty with the US or not.

You’d still be able to credit foreign taxes paid against any US tax owing, on income anyway, treaty or not.

Where you get screwed is when countries have different philosophies on things. E.g. Canada doesn’t tax gains on your home, but you can’t write off mortgage interest on your taxes. Meanwhile USA taxes gains on your home but lets you deduct mortgage interest.

If you’re a dual citizen living in Canada, you pay both.

Or if you live in a country with predominantly sales taxes and no income taxes, well, now you get to pay lots of sales taxes and US income taxes.

Not only the US, but if you've ever claimed residence in California, they might decide to tax you for foreign income as well (if you accidentally leave any part of your life there behind when you move on, for example, leave a car registered there, or keep medical records with your doctor, even visit family there too often)! So add another potential 14% for high earners.