By law the US government cannot permit default. Does that give the executive the power to trump limits on the Fed?

We'll see.

Others argue minting is more palatable. I think legally that's true. I think politically that's false: there is a visceral reaction to any talk of "printing." The various euphemistic ways the Fed can handle it will be preferred. Of course it will end up in front of SCOTUS, but that's a political win: SCOTUS becomes the bad gus trying to "destroy democracy". Or something.