Gandalf and Sauron

Sauron is only one Istari,and he is handicapped because he put most of his power into the one ring. Could not all the Istari combined overthrow Sauron. The blue wizards, radagast , gandalf,and saruman are all maiar. So they should be able to pull it off.
---mordor

let me just say that sauron was not an istari, for there were only five. gandalf, saruman, radagast, alatar, and pallando.
you could say that if the wizards should combine their powers to overthrow the dark lord, they would win.
But to reiterate what a few have been saying, its purely skeptical. They were sent not to fight power with power, but to educate and urge the free peoples of middle earth to fight sauron in some way. And if their powers were constrained, then it becomes doubly hard to speculate.