How can Iago be blamed for Othello's downfall?

Iago is almost entirely responsible for Othello's downfall. From beginning to end, Iago orchestrates the entire dastardly scheme that brings about Othello's disgrace and demise, starting with the alienation of Cassio, Othello's trusted lieutenant. After humiliating Cassio, Iago begins convincing Othello that Cassio and Desdemona are having an affair, a claim bolstered by his famous handkerchief trick (another deception fueled by Iago's machinations). Finally, wrongly convinced that Desdemona is involved with Cassio, Othello kills her. Once he discovers his error, Othello kills himself. This tragic series of events is caused by Iago's deception, so he can be seen as the primary cause of Othello's downfall. Indeed, much of the play focuses on Iago's construction of his vile plan, and the nature of his scheming is both fascinating and disturbing. As such, the play not only focuses on Othello's tragic end, but also on the way Iago causes it through his elaborate deception.