Milley's challenge: How do we stop presidents from committing nuclear genocide?

I agree with a lot in this piece by Tom Z. Collina of the Ploughshares Fund: 

Just after the January 6 attack on the U.S. Capitol, Gen. Mark Milley faced an impossible choice: should he allow President Trump to retain sole authority to start nuclear war, or should he intervene to block such an order?  

Unfortunately, under existing policy the only way to safeguard the nuclear arsenal from an unstable president is not to elect one. Once in office, the president gains the absolute authority to start a nuclear war. Within minutes, the president can unleash hundreds of atomic bombs, or just one. He does not need a second opinion. The defense secretary has no say, and Congress has no role.

In retrospect, voters should never have entrusted Trump with the power to end the world. But do we really think any president should have this power? By now, it should be clear that no one person should have the unilateral power to end our civilization. Such unchecked authority is undemocratic, unnecessary and extremely dangerous.

But I'm skeptical of his proposed solution:

President Joe Biden needs to fix the system for himself and all future presidents.

First, Biden should announce he will share authority to use nuclear weapons first with a select group in Congress. The Constitution gives Congress the authority to declare war, not the president. The first use of nuclear weapons is clearly an act of war.

Second, Biden should also declare that the United States will never start a nuclear war and would use the bomb only in retaliation.

Leaving aside whether the U.S. should declare a first-strike off-limits -- something that should happen, but I'm skeptical will -- Collina's fix basically involves the problem he identifies in the first place: It requires continuing to elect non-nutty presidents. That's far from guaranteed. 

Biden could announce that he'll share nuke authorities with Congress. Subsequent presidents could revoke that pledge, though -- and if they're anything like Trump, they probably will. The only real way to limit a president's power over nuclear war is for Congress to pass a law.  That hasn't happened yet, either, but perhaps Gen. Milley's experience will persuade enough members that it's time.