Why didn't 👁️Sauron send all of the 💀Nazgul to Isengard?

[BalrogRingDestroyer]

In Return of the King, Sauron freaks out and sends the eight remaining Nazgul all toward Mount Doom to try and prevent the Ring's destruction. Of course, for the side of the good guys, it was luckily too late for the Nazgul to get there in time.


However, if Sauron truly thought Saruman had the Ringbearer, and presumably, by extension, the Ring with him, it would seem that the thought would have to cross his mind "What if he uses it against me?" Given Gandalf's remarks that Sauron WOULD expect someone to use it rather than destroy it, why didn't he send all the Nazgul and order his entire army to smash through Minas Tirith and storm Isengard to get it back before Saruman could use the Ring's power to start taking over as a rival Dark Lord?

 

[Squint-eyed Southerner]

Saruman was, as Gandalf said, "doubly" a traitor, but Sauron was not yet aware of it; he still saw Saruman as an ally -- a reluctant one, perhaps, but still an ally.

And as Gandalf explains, Sauron's exchange with Pippin made it clear that he believed both the palantir and Pippin himself were in Orthanc. Therefore, one Nazgul would be enough.

My impression is that Sauron sent even the first winged Nazgul only reluctantly; as Grishnakh said:

'But the winged Nazgul: not yet, not yet. He won't let them show themselves across the Great River yet, not too soon. They're for the War---and other purposes.'

Only when Saruman fails to report via the palantir -- for how long, we do not know -- does he send a winged Nazgul to find out what's going on. That's the one seen by Theoden's company at the campsite; he would, of course, have no knowledge of the episode with Pippin and the Stone. A tight spot for Saruman, to be sure, but he probably wriggled out of it by claiming to have been wrapped up with launching his spoiling attack on Rohan, together with a promise to report soon; he too, would be unaware that Pippin had revealed himself to Sauron.

We never witness either confrontation with Saruman, but of the latter, Gandalf speculates:

'A messenger has been sent to find out what he is doing. And after what has happened tonight another will come I think , and swiftly. So Saruman will come to the last pinch of the vice that he has put his hand in. He has no captive to send. He has no stone to see with, and cannot answer the summons. Sauron will only believe that he is witholding the captive and refusing to use the stone. It will not help Saruman to tell the truth to the messenger.'

It would be after receiving the report from this second Nazgul that Sauron would consider Saruman a rebel, possibly in possession of the Ring. But by that time, he would already have seen the Heir of Isildur in the stone, and know it was no longer held by Saruman. In which case, he would likely believe that Aragorn now had the Ring as well-- as Aragorn no doubt intended. It was this that precipitated Sauron's premature attack on Gondor.

So you could say that the stone, the hobbit, and the Ring did cause Sauron to "send all the Nazgul and his entire army" -- just not against Isengard.