How can Iago be blamed for Othello's downfall?
Iago can be blamed for Othello's downfall because it is his innate evil, bitterness, jealousy, and resentment towards the general that leads him to initiate an evil plot, not only to punish him but to get rid of him completely. Iago's ill-feeling towards the general exists even before Othello's appointment of Cassio as his lieutenant. At the beginning of the play, Iago informs Roderigo that Othello's promotion of Cassio instead of him is what gives him cause for revenge. The appointment, however, is just the catalyst Iago needs to set him on his journey of destruction.
From his point onward, Iago sets about lying, deceiving, manipulating, and misleading others (including Othello) so that his lust for revenge and his inherent desire for malice may be satisfied. He first uses Roderigo to convince Brabantio, Desdemona's father, that Othello has kidnapped his daughter and is molesting her when, in fact, she has decided to elope with the general because she loves him. The deceived Brabantio believes Iago and Roderigo's lies but fails in having Othello demoted or arrested when his daughter comes to her love's defense. The embittered Brabantio then plants a pernicious seed in Othello's mind by telling him that he should beware for, if his daughter could betray him, she might betray him as well.
Othello's transfer to Cyprus provides Iago with the ideal opportunity to further his plot. He cleverly draws Cassio into a brawl by using Roderigo, and when the lieutenant is dismissed by the general, Iago deviously concocts a plan to convince Othello that Cassio is having an affair with Desdemona. He tells the unsuspecting ex lieutenant to ask Desdemona to intervene on his behalf and speak to her husband about his reappointment.
Iago loads his rhetoric with innuendo and suggestion when he talks to Othello. He also gains his trust and confidence to such an extent that the general emphatically believes that he is acting in his best interests. When Iago sees, for example, Cassio trying to leave Desdemona's company surreptitiously, he declares "Ha! I like not that." His statement immediately piques Othello's interest and Iago cleverly plays him until the general is suspicious of Desdemona's association with Cassio.
To confirm Othello's suspicions, Iago speaks of an incident where Cassio had exposed intimate details about his supposed affair with Desdemona. He plants a precious gift that Othello had given Desdemona, a handkerchief, in Cassio's rooms. When Othello eventually sees the object in Cassio's girlfriend's hands, he is convinced. He vows to murder his wife in her bed while Iago will take care of Cassio.
Othello later suffocates Desdemona, believing that he is ridding the world of her manipulation and saving other men from being hurt by her. When he is confronted with the truth, reported by both Iago's wife and a letter written by Roderigo in which he exposes Iago's machinations, Othello cannot bear the guilt and pain for having wrongfully murdered his innocent wife and commits suicide.
In the end, though, it is fair to say that Iago would not have had so much sway over Othello if the general did not feel insecure about his foreign status, his age, and his race with regard not only to the esteemed position that he had acquired in Venetian society but also his place as husband to the beautiful and young Desdemona.
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.