> The president's authority over the military is a legal fiction

No, its not; and its kind of odd to say that during the era when not omly does the President fully exercise that power, they have for all practical purposes had it augmented by delegation (substantively on paper, and even more broadly in practice) of Congress’ power to declare war.

It’s true that most Presidents don’t micromanage the military, but they very much do command it, and a power generally used with some discretion and reserve is not the same as a legal fiction.

But the important thing about the President’s Commander-in-Chief role is not that it is a power (though it is), but that it is a constraint on the Congressional power to orgabize and set rules for the military.

I can guarantee you that there have been times where the top military brass walked into a meeting with the president with 3 options and left with an order to come up with something better. I have no insider knowledge but at the end of the day the president has the final say. Now I don't know how frequently the president overrides his military advisers but it must happen.

For an extreme version of this, see Truman relieving Gen. Douglas MacArthur of his command during the Korean War.

Not only that, but it's not like the head of state is alone with the military brass in such meetings. There will be people there both from the permanent civilian bureaucracy as well as advisors of some type from the party in power.

Ultimately, military grand strategy is a domain of politics as much as it is about how to wage war. The agendas and objectives are ultimately continuations of political goals of whoever is in power. During a war, the fighting must be coordinated with diplomacy, economy/trade/manufacturing and public relations/propaganda, all of which generals tend to know little about.

And even if the President is not the one making the micro decisions, he/she definitely is responsible for making sure the war is waged in a way that is aligned with the general objectives of the administration.

This means defining objectives, access to resources as well as defining the rules of engagement. And equally importantly, listen to the military and determine when the time is right to actually provide additional resources or permissions, despite political costs.

That's true in practice. So in theory, if the president wants things badly enough, he can keep push harder and also keep firing and hiring people until he gets what he wants.

Of course, that style is a lot harder, and thus consumes a lot more limited attention.

Perhaps. But it does prevent Latin America (and elsewhere) style military rule.

Instead we get military generals who act more like politicians the more senior they get (proven by study). And it seems that often politicians with little to lose and a lot to prove are often more hawkish than the military around them (Hilary Clinton, Wolfowitz, et al).

But, you know, tradeoffs…

And the President can always fire their asses if he feels like he isn't getting good counsel.

> The president's authority over the military is a legal fiction

Having served in the US Navy, this statement could not be more wrong. All command authority is delegated from the President, full stop.