Military capacity
While much is being made of how extended we are with ground troops, it's easy to forget that there are a lot of carriers, bombers, submarines, missiles, bombs, and other hardware, along with the personnel to run them, more or less sitting around on their backsides right now. Just because their mission was accomplished doesn't mean they can't take on a new one.
Hostile nations assuming we can't take on any more might do well to remember that.