how does atticus respond to the trail?

Do you mean when he is first offered the case or after the trial is over?

After the tom Robinson trial is over

Atticus is pretty crushed. There was always the sense that he was destined to lose the trial no matter what, "Simply because we were licked a hundred years before we started is no reason for us not to try to ..." Atticus still held out hope that for once, the truth would outlast ignorance and bigotry. Atticus presented an open and shut case. Even a child could see through the Ewell lies but the white jury, in the end, went with their bigotry. I think Atticus felt discouraged over his friends and neighbours as well as the law which he held so sacred: both had let Tom Robinson, a clearly innocent man, down.