The Power of Isengard

[Voralphion]

Although it may have taken him a while, Saruman would have been able to master the ring and in that would have overthrown Sauron. Having mastered hte ring he would have been able to take control of Sauron's forces, including the nazgul and would have defeated the forces of good. The result would have been the same as if Sauron had regained the ring except the power would have been in Isenguard not Mordor.

[Tuor of Gondolin]

The situation might have been even more complicated related to the Ring.
Discussing Frodo taking the Ring, in Letters #246 JRRT observes:

Would they (the nazgul) have been immune from its power if he claimed it as an instrument of command and domination? Not wholly. I do not think they could have attacked him with violence, nor laid hold upon him or taken him captive; they would have obeyed or feigned to obey any minor commands of his that did not interfere with their errand-laid upon them by Sauron, who still through their nine rings (which he held) had primary control of their wills.

But as to who would control Sauron's other forces, Saruman with the Ring or
Sauron with close proximity and the nazgul????? And of course, JRRT's above
musing was in Sep., 1963, and therefore probably not quite canon.

Oh, and how about this for tactical speculation: either the nazgul on their
pteradactyls or Dunedain with eagles pull off a commando raid landing on top
of Orthanc (like the German army in 1940 at Fort Eben Emael in Belgium or Otto
Skorzeny rescuing Mussolini in 1944). Orthanc might have weak spots like the
gate of Minas Tirith on its roof or balcony windows.

[Eomer of the Rohirrim]

Where are you guys getting the information that Saruman could have, in any way, overthrown Sauron using Sauron's own Ring?

[Boromir88]

Eomer, one on one, Saruman could not have defeated Sauron, as Letter 246 points out. But, if Saruman could summon himself an army he could overthrow Sauron. However, I don't see how Saruman could be able to do that, in the amount of time he would have.

[Eomer of the Rohirrim]

Saruman did have an army. It would have been just a small nuisance, however, that Sauron had a truly vast army.

[Boromir88]

Very true , but Saruman could have the same plans as Galadriel or Elrond. Once owning the ring, taking it summoning a GOOD enough army to be able to overthrow Sauron. As for me, I think his arrogance wouldn't have done that. He saw himself able to wield the ring, and would have tried to take on Sauron, of course utterly failing. But that's my opinion.

[Tuor of Gondolin]

I think Saruman is being rather underestimated in this thread. While there is
considerable doubt about Elrond, Galadriel, Aragorn, et. al. defeating Sauron
using the Ring, Gandalf and Saruman were Maiar on, I believe, an equivalent
level with Sauron and could therefore have been essentially his equal, once
they would ignore the ban on their using their powers openly in Middle-earth.