...and what exactly will they do about it? The question is about decentralized exchanges. Countries may choose not to "tolerate" whatever they wish, but the internet is under no compulsion to tolerate shortsighted countries.
They can prosecute the operators of those sites, not like it didn't happen in the internet before. Usually some things survive, but at the cost of extra hurdles (e.g. only accessible via tor, but even there, some people got busted through bad opsec).
You mean the operators of web front-ends which provide access to the exchange? I suppose that's possible. But I don't know how long that will even be the main way that people access them.
They would need to regulate every ISP in the country to block the protocols, and then go after every website just using those protocols under the hood (and most of these would not be in the USA).
I can't see that ever happening especially because these protocols would have non currency uses as well.
Regulate people using handcranks to power portable transmitters transmitting information at variable frequencies to be received and picked up by those who know of beamforming and antenna design.