[Dakêsîntrah]

The Witch-king's vulnerablity to destruction is clear: he was rendered impotent by two mortals.

So you're inferring the Westernesse blade is able to 'kill' something neither living or dead? How does that work? I think Tolkien may have created for himself a little paradox.

I just don't think it would be in the nature of a sword, no matter what kind of magic enhances it. A sword is made to ultimately kill even in Tolkien's universe, but a physical weapon terminating a spiritual being is not logical.

Gandalf had Glamdring, but that apparently would not have any real effect on the WK.

So the Witch-king would temporarily stun Gandalf and mow him down with the flaming sword.

He may have had a notion of who or what Gandalf the Grey was, but the contemptuous tone in which he adressed Gandalf doesn't sound to me as if he had any idea how his opponent had been changed and enhanced by being resurrected.

Rather it seems to me that regardless whether WK went up against Gandalf the Grey or Gandalf the White, he would still have a chance at beating him with the enchanted sword. I think he could care less who Gandalf was bodily; but I don't think he was stupid enough not to realize Gandalf's innate divinity had risen in his Spirit. What the Witch-king could do however is wrench Gandalf's bodily authority or reputation away from him. And again, render Gandalf useless without bodily form.

But if that was so, it's rather a strong argument against the WK's ability to break it.

I don't see that at all. If we want to say one of Gandalf's sticks were fashioned in Lothlórien, why would something wrought from nature be impossible for WK to break?
I think it's impossible, yes, for WK to wrench Olorin's authority away as a Maia, but in the weak, flawed, flesh of Man it is possible.

On a side note, I really don't believe the Istari came into Middle Earth for the first time wielding staves. Their power was innate.

Just like Gandalf could only break Saruman's staff after he'd been sent back and empowered as the new White Wizard,

I think the Istari always had potential to usurp authority from themselves, so in the case of their wills to break another's staff, for example, it would not be possible unless one of them transgressed the purpose and responsibility of the Valar and ultimately of Eru. Saruman transgressed divine fiat and was judged accordingly.

Saruman could have easily broken Gandalf's staff at Orthanc. But Saruman is more cunning than to declare himself as having turned to the dark side. Rather he has convinced himself that evil, even Sauron, is really not evil, but a maligned interpretation of good that people have created and are thus ignorant of. And so, maybe his digressions with Gandalf can be negotiated to reach a compromise. Gandalf of course refuses, and so Saruman tortures and tempts his mind by imprisoning him on top of Orthanc.

To the Witch-king, a mere stick wrought from that world would be no trouble to break. It doesn't have any special magic enhancements that could resist him, that I am aware of. If a physical body can be broken, so can a physical object from that same universe. If the WK is neither living or dead, why should he fear breaching natural (physical) authority by breaking its physical product or symbol?

That must have been in the movie. In the book he said nothing of the sort.

Yeah, I was referencing the movie.

Gandalf resurrected being killed a second time by the WK would be much like Jesus dying on the cross a second time after his resurrection.

In all respect, I did say that to some degree there are obvious parallels. The nature of both figures are more parallel than the events that surrounded them.
And of course, it depends on your theology, but some Gnostics, or I should rather say, Pneumatic sects, called by their ancient name-- did in fact believe Jesus would die and resurrect a second time. But that's beside the point, I think

but I just don't see any chance of him prevailing against Gandalf the White.

Not prevailing in what sense? Gandalf's innate divinity had risen, which I think was a separate thing in regards to the incarnation of his second body. It was the same body essentially, just the hair color changed and he was dressed in white with a new walking stick, presumably carved from the Elves? I don't see anything drastically different *physically. if you can point me to a text, I will be obliged to concur.

So not to hold forth any false modesty, it really is true that I am less knowledgeable and more hazy on the books than the movies. The movies I have down to a tee, having watched them for the umpteenth time, plus every little nook and cranny of the EE.

Thanks for responding to my rambling.

Best Regards