One possibility is they can outlaw the nodes, making it illegal to run a node with severe consequences.
Other possibility is block at protocol ISP level on massive scale.
Is this possible ?
Practically: yeah sure no problem. Governments already collaborate on stuff like missing people and/or terrorist tracking and civilian espionage.
On a legal basis though... where's the law that prevents me from doing the kind of math to run a bitcoin node?
And even if there was such a law, it might be unconstitutional and thus not enforceable (at least in the long run).
Realistically? No.
We still have bit torrent don't we?
Never underestimate the capability of other people to ruin your day.