Joseph Cotten did not receive an Oscar nomination for portraying Jedediah Leland in Citizen Kane.
Cotten does something rather interesting with his work in that he makes Jedediah the only character in which we are allowed to connect. Welles leaves Kane as a distant figure even though he is the lead. I would say this is purposeful though order to make us keep looking for the truth of the man just like the reporter we follow trying to find out the meaning of Kane's last words "Rosebud". Cotten fulfills an important need of the film to have the man who is genuine. It won't be found in Kane, or Sloane's Bernstein who's essentially a boot lick, and certainly not the reporter since we only see him from behind or in shadow. Cotten in the earliest scenes in the chronological sense gives an effective depiction of the earnestness of wanting to make a statement in the world, while clearly not having the ego about in that Kane does. Cotten does well to essentially let us in on the world of creating the newspaper through his calmer and less presumptuous portrayal of Jedediah. It's very intriguing that even well hanging on the side of the frame Cotten is able to create the man who's far more easy to relate to than Kane is.
Cotten is very good as he reflects and really amplifies what Welles does with Kane in every step of Kane's downfall as a person. As the paper grows Kane seems to become engulfed into his own success whereas Cotten portrays Jedediah still as the same man as he was when they entered the office, but with perhaps a bit less enthusiasm as he watches Kane become a bit too proud of his accomplishments. Cotten says a great deal in his reactions and quiet comments about what is happening to Kane. He expresses well a genuine concern as he still expresses the optimism of the original thought behind the paper while Welles's Kane seems all the less authentic as a man. Cotten still brings the passion though as Jedediah campaigns for Kane's run for the governor of New York, and makes it all the more affecting when he shows the especially genuine disappointment in Jedediah as he sees Kane fall due to Kane's own vices. Cotten expresses well the lost of the faith of essentially the promise that Kane made to him repeatedly about the work they were going to do together. Cotten portrays this to be a final straw for optimism really as the later set scenes with him, Cotten portrays Jedediah as basically jaded individual who no longer seems to have the passion for much of anything, as even when he fires Cotten shows it to be more of a sigh of resignation than any sort of outrage. Cotten powerfully brings to life the loss of Kane's dream by having Jedediah figure out that it was never possible. Now I should briefly mention the framing the flashback scenes where the reporter interviews Jedediah as an old man. Cotten might to the old man mannerisms a tad too much, but really in terms of unneeded theatricality Cotten really seems pretty subdued compared to some of the other performances. In addition Cotten makes up for it with his very strong work in the flashback scenes as he creates the character arc we connect with that brilliantly echos the colder one presented by Welles.