Mauhur and his lads
 

If memory serves correctly Gandalf was in Fangorn at the same time as Mauhur and his "Lads". Why didn't Gandalf use his powers to stop them?

Maybe he did... plainly they were of no help to Ugluk

Let's not forget Fangorn is quite big. Treebeard and others were also there and did nothing. That's one thing; second: even Saruman (or his "ghost", apparition, whatever it was) was out there (a bit later) and nobody did anything (although it is true that one apparition of Saruman probably does much less noise than a band of warriors). Last of all, however: didn't, by any chance, Gandalf just at that point stand "on a high place" and battled with his will against Sauron in order to turn him away from Frodo? I believe this particular event occured just when Gandalf was in Fangorn. Somebody correct me if I am wrong. But it was certainly supposed to happen around that time, and I think in some timeline draft of Tolkien's it was even confirmed to be that way.

I always interpreted it that he was helping Frodo on Amon Hen. :confused: It would make sense based on Frodo's own experience of two conflicting forces trying to push him. So this would have had to happen a couple days before Mauhur and his lads were running through the woods, and most likely on a different high place...

But maybe I'm forgetting something else and you're right, he was just constantly hepling Frodo resist Sauron's will.

Last of all, however: didn't, by any chance, Gandalf just at that point stand "on a high place" and battled with his will against Sauron in order to turn him away from Frodo?

In unpublished notes T said explicitly that Gandalf was "on a hill in Fangorn" when he strove with the Eye over Frodo on Amon Hen. This was two and a half days before "Mauhur and his lads" attempted to break the Riders' leaguer.

And, yes, it's true that Fangorn is quite big, 100 miles from east to west and even more north-south: as big as the whole Shire, and nearly the size of all of Mirkwood south of the Narrows. It's a bit like saying "They were both in Denmark, surely they must have seen each other."

Looking at Gandalf's actions throughout The Hobbit and LOTR, we don't see him seeking out swarms of armed enemies to personally destroy. Such actions very possibly were prohibited to the Istari, unless in self-defense, to avoid potential power-drunkenness.

Well, it probably also took them a while to get to that place first, and also, maybe after an exhausting "battle of wills" and other stuff (trying to figure out what is happening, what is the forest doing, and what is the general situation since I've just returned from the dead a couple of days ago) Gandalf wasn't so keen to rightaway go and pursue some random Orc warband (of which there might likely have been more around, e.g. some random wood-gatherers or scouts).

Yes, that was the one I meant. Thanks for providing that.

And yes, basically that was what I had in mind. We tend to see Fangorn as "oh, one forest, like the one near my house, where I take a walk for half an hour every afternoon". But Fangorn was essentially the size of a whole (smaller) country.

And Inzil's point is also quite a good observation, I'd say.