One of the difficulties of modern military preparedness is that there are many possible conflict areas spread around the globe. Thus, the U.S. needs to be able to project power in one area while still being able to maintain a credible threat in others.
For example, let’s say that we decided we only needed one carrier group. And sure, that would probably be enough to handle any forseeable conflict in the near future. So we decommission our carriers and leave the Nimitz steaming around out there.
So what happens? Let’s say tensions are high between, say, India and Pakistan. Then a conflict erupts in some other part of the world, and we send out carrier group there. This may well precipitate a war between India and Pakistan, because they now know that the U.S. can’t do anything about it.
As the number of these potential regions grows and conflict zones erupt all over the place, you really need quite a large force to be able to deal with them, plus meet your UN commitments, plus maintain a reserve force as a deterrant.
Also, the military is underpaid, and weapons systems are aging and need to be replaced. Flight hour cutbacks means pilots aren’t as sharp as they should be.
Saying, “We should cut the military budget” is easy. Actually sitting down with your red pen and figuring out what to cut is the hard part.
Note that neither candidate wants to cut the military budget.