Saruman for or against Sauron?

It might be that all things that become under Sauron's command eventually become under his control through his power, as with the fate of the Nazgul and the Mouth of Sauron, for instance. They are very much Sauron's puppets, doing exactly as he bids, and Saruman may have sensed that this was to be his doom unless he strove for the power of the Ring itself, his ''way-out" from Sauron's clutches.