Let me tell you something: it won’t be long at all till the left is insisting that people in these countries be allowed to vote in American elections. The supreme court will be taking a very close look at the idea, and their reaction will not be at all unfavorable.
The argument will be along these lines: America, as the world’s only remaining superpower, has such an overwhelming effect on the lives of people abroad that they should be allowed to vote in our elections, out of a sense of fairness.
They're already doing it.
Here's one example.