sauron and saurman

[The Saucepan Man]

Sauron was playing Saruman like an old violin. Saruman needed to get close to the Dark Lord to have a better chance at finding the ring. Sauron saw through it, but also saw his chance to use this pawn(meaning Saruman) as an extra piece in the war.

Sauron's plan might well have backfired, though, if Saruman had actually got hold of the Ring (and he very nearly did, but for a touch of mistaken Hobbit identity and a group of rogue Rohirrim).

I'm not saying that Saruman with the Ring would have defeated Sauron, but he would certainly have presented (to use the current parlance) a credible threat.