If “fears US aggression” is code for “fears reprisals from the US if they try the same thing with Taiwan” then your first sentence is correct.
The US military existing and being ready to respond has historically kept a whole bunch of other players behaving more peacefully than they would otherwise do. The problem is when you get an unpredictable administration in power, which is when other countries start testing the waters and the US military is used unwisely.
If “fears US aggression” is code for “fears reprisals from the US if they try the same thing with Taiwan” then your first sentence is correct.
The US military existing and being ready to respond has historically kept a whole bunch of other players behaving more peacefully than they would otherwise do. The problem is when you get an unpredictable administration in power, which is when other countries start testing the waters and the US military is used unwisely.