Sauron and Istari

[Inziladun]

Originally Posted by Sarumian

Sauron could hardly consider Gandalf weak after him killing a Balrog (or the Balrog was also weak and there was some contagious weakness that pursued Maiar in Middle Earth).

I think it's doubtful Sauron knew anything of the contest between Gandalf and the Balrog. The community of Orcs in Moria seems to be a pretty self-contained unit, not having much to do with outside events. There is no evidence the Balrog ever left Moria after it entered, and Sauron apparently never went into the Mines. From that, Sauron could have had only a passing knowledge of the Balrog, and maybe not even that; for if he knew it was there, would he not at some point tried to reach out to it?

Originally Posted by Sarumian

But later Gandalf The White, as we remember, struggled with Sauron (so they had a personal encounter!) sitting at Amon Hen. As I can remember, Gandalf was distracting Sauron from Frodo, thus he should have employed a formidable power to attract Sauron's attention and keep struggling for a long time.

Gandalf tells Aragorn, Legolas, and Gimli that he "sat in a high place, and I strove with the Dark Tower; and the Shadow passed".

But he later says, when discussing the recovered Palantír of Orthanc

'Maybe, I have been saved by this hobbit from a grave blunder. I had considered whether or not to probe this Stone myself to find its uses. Had I done so, I should have been revealed to him myself. I am not ready for such a trial, if indeed I shall ever be so. But even if I found the power to withdraw myself, it would be disastrous for him to see me yet--until the hour comes, when secrecy will avail no longer.'

TT The Palantír

That shows a clear difference between Gandalf's action in distracting Sauron from Frodo, and outright revealing himself. Sauron seemingly did not know Gandalf was behind the turning of his Eye from Frodo.