In To Kill a Mockingbird, how does Atticus show compassion toward Tom Robinson?

Atticus shows compassion toward Tom Robinson in two primary ways. 

First, by taking his case. Yes, the case was assigned by Judge Avery (although court-appointed defenses were usually assigned to Maxwell Green, the new kid, who needed the practice) (246), but Atticus would have taken it anyway, because he knew he was the best chance Tom Robinson had (and perhaps the best equipped to deal with the fall-out, considering how calm and level-headed he is). 

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Atticus shows compassion toward Tom Robinson in two primary ways. 

First, by taking his case. Yes, the case was assigned by Judge Avery (although court-appointed defenses were usually assigned to Maxwell Green, the new kid, who needed the practice) (246), but Atticus would have taken it anyway, because he knew he was the best chance Tom Robinson had (and perhaps the best equipped to deal with the fall-out, considering how calm and level-headed he is). 

Second, he shows compassion when he goes downtown the night Robinson is moved to the Maycomb jail before the trial. He knows the racism which surrounds him and the lynchings which follow them--lynchings which were committed on the mere hint that a black person had done something wrong, or in the words of some white Southerners of the time, "just to remind them who's in charge"--and knows a lynch mob will form. After all, the number one "reason" for lynchings at that time was the accusation (without proof) that a black man had "outraged" a white woman. Atticus thus risks his life in his compassion for Robinson.