If other countries close their borders to America how is Trump going to deport?

Trump is claiming he's going to deport millions of illegal immigrants. But that would mean arrangements would have to be made with the receiving countries. They could simply refuse to let passengers off the plane/bus/or whatever or even refuse them permission to cross the border.

Given these immigrants won't have documents a country could easily argue they weren't originally from there thus they have no legal responsibility to take them.

A migrant could also argue he was born in the USA but the government wiped his proof of citizenship. Given so much such as driving licences are stored on computer that wouldn't be hard.
If other countries close their borders to America how is Trump going to deport?
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