Well, here's the 'straight skinny'. If you give a President a large, robust armed force, there's an awful temptation to — you know — use it. For that reason, Article I, section 8 ("Congress shall have the power to...") allows them "To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years; To provide and maintain a Navy."
Got that? We can have a permanent (standing) NAVY, but not a similarly situated ARMY. Why? Because it's hard to institute martial law with just a navy, and it's next-to-impossible to go adventuring in tropical climes with just a navy. Yeah, you can shell the beaches and coastal towns, but after that it's pretty much over.
Now, I know (and I've actually had the argument used against me) that one can't survive in the modern world without the ability to 'project force', although most other nations seem to be doing just fine without a DOD whose budget makes it the seventh largest economy in the world.
So that's where we are today: every President back through Harry Truman, including Eisenhower who warned us about "the military-indutrial complex", have used their large, robust army to project force throughout the world: Korea, Iran, Cuba, Africa, Eastern Europe, Southeast Asia, the Caribbean, the Middle East... did I miss anyone? And along the way we have caused a substantial amount of collateral damage and cultivated entire cultures of people willing to commit suicide as long as they get to take a few (dozen, hundred, thousand, million) Americans with them.
And our solution to this problem: obviously, we need a larger, more robust army, plus DHS, plus TSA, plus plus plus plus plus.
Allow me to suggest an alternate plan. We cut the Pentagon budget by 82%. We use the remaining 18% to repatriate all our overseas troops and their expensive equipment and to refuel/rearm all our naval ships. We stop solving everybody else's problems and concentrate on solving our own. For the few thousand core members of the army that enable us to train an army when/if we ever need it, we make sure that they understand the nature of their oath: that they swear to follow the Constitution, and the orders of their superiors in support of that same Constitution.
This could lead to odd situations, it's true. The President orders the First Marine Division into the surf off Latakia, and the General in charge asks for a copy of the Congressional Declaration of War against Syria so he can show it to his gyrenes. The President says "Well, actually, there hasn't yet been a declaration of war on Syria." and General Jarhead tells his boss to let him know when it happens, then stands all his Marines down because they're going nowhere until Congress agrees to pay the bill (on your behalf).
Fantasy, of course. Most of our military join up for the express purpose of making loud noises. Where's the fun in not being able to airdrop into a third-world country and shoot the place up?
Here's the fun: it almost all goes to the American civilian population who no longer get taxed as heavily (because we don't spend so much on expendables), we're thus able to afford luxuries like foreign travel, and we get to go to the airport and get directly onto our airplanes without having our crotches inspected, and we get to visit countries like Cuba with new and interesting customs, and when we get there people don't sneer at us; they (in fact) smile because the US dollar is now actually worth something.
I'm trying to find the downside to this plan. I know there must be one; I just can't see it. Help me out here.