“Why is deploying to international waters viewed as threatening?”
The US Navy is the most frequently deployed diplomatic “stick” used by the President to enforce freedom of the seas. The threat of the Navy’s presence stops stronger powers from threatening weaker powers with “sanctions” intended to force coercion. The Navy doesn’t even need to be there at the moment. Just the threat that it can be there is sufficient. Because China does want to be threatening to its neighbors, this deployment is viewed by them as a threat to their threat.
“used by ANY President to enforce freedom of the seas and US POLICY”
Just a little more accurate... (of course this did not apply to the jug-eard Executive Anus)