They can easily, legally block things in the USA for USA ISPs.
They risk sparking a diplomatic incident if they were to try to take down a .ccTLD domain. Non-USA based root servers would not have to abide by USA rules, and in fact, local websites might get court injunctions to force ISPs to continue to resolve example.xx into what ever was there before. This means whether a domain resolves depends on what DNS servers you talk to.
What your describing might fragment the DNS system into multiple different ones.
They risk sparking a diplomatic incident if they were to try to take down a .ccTLD domain. Non-USA based root servers would not have to abide by USA rules, and in fact, local websites might get court injunctions to force ISPs to continue to resolve example.xx into what ever was there before. This means whether a domain resolves depends on what DNS servers you talk to.
What your describing might fragment the DNS system into multiple different ones.