Back in colonial times it was very feasible to keep the executive in check. Nowadays it is a technological fact that the executive needs nuclear authority just to be in a position to make a timely counterstrike effort.
At least, this was the dogma last I checked, maybe there is enough interdiction capability now to change this dynamic. I would be delighted to learn otherwise, but given the necessity of secrecy in these things any evidence must be compelling.
That said - Until the logic of MAD ceases to prevail, there is an insane sort of game theory rationale for an executive with extensive powers, regrettably. It's hard to see how to get past the eventual nuclear war scenario without a one world government. With nukes we are walking a tightrope, but we cannot reasonably expect to do so indefinitely.
I'm only pointing out that nukes are fundamentally a threat to the rule of law. We can't invent a world without them just yet, but we should at least think of them as a systemic threat to the world we're trying to create