Physical bodies and 'Mortality' of the Istari vs other embodied Ainur

Question

The Istari were "clad in the bodies of Men, real and not feigned", unlike most Ainur who were inherently spirits and used bodies "only as we use raiment".

However, Morgoth became permanently embodied in his attempt to dominate Arda's physical matter, and the same happened to the Balrogs.

Something of the sort probably happened to Melian, given that she was able to have a child (and it's supported in late writings in History of Middle-Earth), but her return to Aman is somewhat problematic given that assumption. Huan was likely also a Maia, and was physical enough to be killed.

But -- was the embodiment of the Istari the same as these other embodied Ainur, or was it more limiting?

Saruman gets killed with a knife - it seems that that probably wasn't an option in the case of Morgoth or Sauron*, as nobody suggests trying to poison them or sneak an assassin into Angband or Barad-dur. (Beren and Luthien had a sleeping and unguarded Morgoth right in front of them and didn't try to cut his throat or anything.) On the other hand, while Gandalf dies in the battle with the Balrog, he seems to survive much longer than a normal human would - more like the Balrogs themselves, who are killed in physical combat, but only with great difficulty.

*OK, Sauron may not have been permanently embodied, but it took him at least a thousand years to recover last time he was physically killed.

TL;DR: Are the Istari more vulnerable to physical damage than other permanently-embodied Ainur? If not, why isn't this exploited more?

Answer 1

This is a good question we don't really have an answer to. There's a fair amount written about the limitations of self-arrayed bodies ("Notes on Motives" in Morgoth's Ring and Ósanwe-kenta spring most immediately to mind) but little on the Istari and how, or if, they differ.

The best we can do is to observe that even incarnated Valar and Maiar are still, y'know, Valar and Maiar, and hence have a great deal of inherent natural power. You've already mentioned this in discussing Gandalf and the Balrogs, but this applies to Morgoth, and presumably to Sauron, as well:

We speak of [Melkor] being 'weakened, shrunken, reduced'; but this is in comparison with the great Valar. He had been a being of immense potency and life.

^{History of Middle-earth X Morgoth's Ring Part 5: "Myths Transformed" Chapter VII "Notes on motives in the Silmarillion"}

The Istari seem to retain much of their angelic power even in whatever form they're stuck in, but it's notable that, by the time of his death, Saruman seems to have lost the greater portion of his. How this actually worked is unclear:

• Perhaps it was removed by some action of a higher power (whether Gandalf, or someone greater still). If so, this would suggest a limitation only imposed upon the Istari, since we don't see this happen against any of the other Bad Guys in the Legendarium
• Perhaps he "pulled a Sauron" and externalized his power into some physical matter; if so, we can't be sure what it was, though the Uruk-hai are as fair a guess as any
• It may be that he was weakened merely by his evil deeds, something I've touched on before; though, if so, it seems strange that he (evil for only a couple hundred years) should be weaker than a balrog (evil for tens of thousands of years)

It appears as though a body's relative weakness is related to the potency of the angelic spirit inhabiting it, but without more information we don't have, it's impossible to say whether or not this was exacerbated in the Istari.