The US government isn't really held back by the Constitution either. It's been diluted so much they can just use Canada as a proxy and return the favour, for example, no problem. I agree with your overall point but it's not really a legal matter, it's just power.

For non-US citizens the US constitution also has no relevance. Thus for non-US citizens it makes no real difference

I'm non-US citizen and still think that there is difference between US and Chinese government.

Tell that to Assange.

... the US government isn't particularly limited in such a way either. They have nice have for everything foreign communications, and all the actions are held as confidential