I am going to take the perspective of during and after the trial, you may mean preceding the trial, but it makes more sense to me to take the former approach.
By the end of the trial, Atticus has done some "stripping." Scout never saw her father sweat and never saw him remove anything before bed, not even a watch. She saw his jacket come off and buttons loosened. She also noted his glistening face. These physical features are not only evidence of the heat, but his uncomfortable feeling about the case.
When he finished speaking with Mayella during the trial, Scout commented how terrible it made him feel to have to get tough and reign questions on her. He had great compassion for her situation, but also needed to defend his client.
After the trial, Maudie and Alexandra comment how Atticus does so much for justice and morality in his town but it hardly causes a ripple. This must make Atticus feel fruitless at times.
Atticus was spat on by Bob Ewell and he just took it. Atticus knew he destroyed Ewell's reputation and Ewell needed to feel like he was getting back at Atticus.
Throughout both the trial and the immediate aftermath, Atticus remains fairly stable. He maintains compassion for others, a desire for equity, a desire for truth, and he holds himself together well. Atticus is perhaps one of the strongest characters written into all literature.