Are all US fighter/combat aircraft constantly armed, even just in training?
As a general rule, unless you are going to use ordnance e.g. training, alert status, or war, you are not going to have it loaded on the jet.  It's just another risk to personnel or equipment out on the line, in hangars, etc.  Aircraft returning with live ordnance are disarmed and unloaded after shutdown and the weapons defused and returned to the bomb farms on base or magazines aboard ship.