Thomas Mitchell did not receive an Oscar nomination for portraying Gerald O'Hara in Gone With The Wind.
The ideal man of the South we meet in these early scenes takes a long hiatus from the film, in fact almost the entirety of the Civil War. When Scarlett finally makes it back to Tara the place is quite barren on the outside, and when she opens the door she finds her father who possibly looks worse. Mitchell is amazing in just how effectively he portrays Gerald terrible state as the wear of the losses over the time Scarlett has been gone can be so well seen in his harried eyes, and haggard face. Mitchell is terrific as he stays so subdued for much of this time yet the devastation of the man is brilliantly realized by him. Mitchell is heartbreaking as he presents the insanity in Gerald as seemingly his own shield against all that his happened to him as there is this attempted glee in him as he speaks of his deceased wife as though she's living, however within the act the original cause of his state can be seen in this sorrow that never leaves him despite his madness's attempt to cover it up. This is until his last scene where his passion for the land once again reappears, and Mitchell once again brings that to life yet now just with this painful desperation in the moment. It's beautifully rendered work by Mitchell and with so many of his performances he proves himself one of the most capable actor in terms of the depiction of the type of extreme emotional states that might leave to some terrible overacting. Mitchell never allows that to be the case giving a striking performance that manages to stand out with this grand epic, as well as marks just the one of his many strong turns from 1939.
Now Ashley's purpose in the story is as the object of Scarlett's affection, as she only sees him despite the fact that he is married early on to Melanie (Olivia de Havilland). Howard does well to really make Ashley the right match for Melanie throughout the film, despite Scarlett's delusion that he should hers. Howard, and de Havilland's work has an unsaid chemistry of sorts given they actually don't share that much time with one another screen. What they do is find the right connection in personal spirit in the way both suggest themselves to be naturally unassuming and unselfish souls. Howard finds the right ease of presence of man who prefers to do the right thing, though states as such in a direct yet quiet fashion. The problem remains though is with Scarlett being constantly smitten with him, to the point that she does not mind how many lives she ruins just to get him. Howard creates the right curious chemistry with Leigh in that he portrays the simple difficulty in interacting with her. He brings the right unease in any of these moments as he manages to suggest Ashley's refusal as man standing in his duty at being a proper husband. When Ashley does reveal that he does love Scarlett in return it's an earned moment by Howard as his delivery is almost that of an unwanted escape of emotion, and depicts a definite guilt within himself after his momentary loss of his usual proper reserve. It's finely measured work by Howard as he keeps Ashley on this certain wavelength of a decent man who is constantly must readjust with his constant interactions with Scarlett. Ashley Wilkes really is a thankless role, in that he's rarely given the spotlight, and he's really there to facilitate the motivations for the other characters. Howard delivers in that respect though giving a supporting performance that truly supports the rest of the cast and the film.