My initial comment stated the goal very strongly. I don't see that an initial stopgap version of it would require a Constitutional amendment. The President's power to federalize the Guard comes from legislation passed by Congress ("Insurrection Act", etc), which Congress could straightforwardly undo. Congress could also reaffirm Posse Comitatus, tighten up any loopholes in the President's ability to divert funding from the state-controlled National Guards. Congress could also include a bit indicating that state courts are the appropriate jurisdiction for claims over control of the guard. The Supreme Council might try to go against that last bit under the guise of "Constitutionality", but the goal would be to give the chain of command stronger grounds to refuse illegal orders.

I'm eager to discuss other avenues of reform, though. What do you see as a minimum viable path to reform?

The President's power to control the national guard comes from the constitution not acts of congress.

“The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States”

But ignoring all that, if a governor used the national guard against federal agents, that’s open civil war. The military gets deployed, and death and destruction follow.

The reform needed is that congress takes back constitutional powers they’ve delegated to the President, and removes a President who violates their will.

Congress has the power to control the President right now. If they aren’t willing to do exercise that authority, there’s nothing we can do.

Let’s say you got Congress to grant states the ability to make war on the federal government in order to provide an extra-congressional check on Presidential power (which I don’t think you can do, but just pretend you can). That’s only useful in a situation where the President has effectively captured Congress. Otherwise an extra-congressional check isn’t needed. But in the case Congress will just remove that power from the states.

This only works even a little bit as a Constitutional amendment—even if you could pass legislation to do it.

The President's power to command the Guard, when called into "actual service of the United States", by Congress. Being called up by a state governor would be in service of that state and would not qualify, right? Hence the constant threat of invoking the "Insurrection" Act.

> if a governor used the national guard against federal agents, that’s open civil war

When state police arrest a fedgov employee for breaking state law, is that a "civil war" ? I would call that enforcing the rule of law under a system of shared sovereignty.

> The reform needed is that congress takes back constitutional powers they’ve delegated to the President

If wishes were horses... Congress failing to exercise their powers for the past several decades is a big part of how we got into this situation. And sure, at any point technically they could retake them. Except it seems that the Republican congresscritters are content with the plausible deniability, while they would be more hesitant to stick their own necks out and positively affirm what's going on.

But the context of reform I am talking about is if the Democrats regain control of the Presidency and Congress. What can be done to make it so that after 4 years of relative sanity regarding separation of powers, people won't just get frustrated and start craving the simplistic answers of fascism again?

A big part of this is the many broken and unjust things about our society, but trying to fix a sizeable number of those in 4 or even 2 years is a tall task. Hence why I'm trying to focus on a kernel of the least possible required to stop the hemorrhaging, so that it might have a chance of getting done before the buntings change again.

> That’s only useful in a situation where the President has effectively captured Congress

Look at the current state of things - Congress doesn't appear to be fully captured, just immobilized.