In To Kill a Mockingbird, how does Atticus protest Jim Crow laws before Tom Robinson's trial?

Atticus protests the Jim Crow laws through his attitude and actions. He is not afraid to go against the code of Maycomb society, and he attempts to teach his children the same sense of social justice. For example, he will not let Scout use the term "nigger". She thinks it's fine because other people in the town use it, but Atticus understands the derogatory nature and the potential harm such a word can do.

The most obvious way Atticus protests the Jim Crow laws is through his relationship with Calpurnia. Although she is his employee, she is not subservient or looked down upon as other people at this time may have looked down on their servants. She is a strong-willed member of the Finch household. In several places, she is described as a mother figure for Scout and Jem. She imparts wisdom, and helps them mature throughout the book. Attics even invites her to stay at their house one stormy night. This level of comfort and equality with black employees was unheard of at the time. When Aunt Alexandria comes to stay, she tries to convince Atticus to fire Calpurnia, precisely because she feels Calpurnia has had too much influence on the children. But Atticus defends Calpurnia's role in their lives, and holds her in the highest respect.

Atticus' first act of protest is accepting his appointment as Tom Robinson's lawyer. Atticus does this even though he knows that the legal battle he is about to engage in is ultimately useless; it is clear that the racist Southern town of Maycomb will condemn Tom before the trial even begins. Tom does not have a fighting chance of winning the trial, yet Atticus makes sure that he does have a chance to be heard in court, even if it will only serve as the first of many stepping stones in the path toward racial equality and justice.

Atticus' second act of protest is to stand guard outside the jail when a lynch mob comes to steal Tom from his cell. Atticus puts his very life and well-being on the line to stand up to the angry crowd and to protect Tom's life and his right to a fair trial. By standing up for the truth, Atticus fights a quiet but important fight.

Atticus is well known by the black people. They believe that he sees them as equal and that he will judge Robinson fairly. He has a reputation for being fair; his father was also a fair man. Atticus protests Jim Crow laws by reminding people that a man is not guilty until proven so in a court of law. The town people already want to declare Robinson's guilt even though they know no facts, only hearsay. Atticus refuses to believe until all the facts are in.

What are "Jim Crow" laws, and how do they relate to To Kill a Mockingbird?

Quite simply, Jim Crow laws are the laws of racial segregation in the United states that existed from just after the Civil War up until the mid-sixties.  They were supposed to insure "separate but equal" public facilities, but basically assured that whites got the best of everything.  (I'll never forget the double water fountain at my high school, one with cold water and one with warm water:  an ancient Jim Crow antique.)  Most everything was affected by Jim Crow laws:  all public places (transportation, schools, bathrooms, drinking fountains, ... even the military!).

The more interesting part of your question is "how do they relate to To Kill a Mockingbird," of course. Well, considering the dates of the Jim Crow laws, you will notice that they exist avidly in the context of the setting of this fine novel.  Although many of Maycomb's citizens are quite happy with the Jim Crow laws, Atticus is not.

Atticus protests these laws quietly, ... and not so quietly, ... in his defense of Tom Robinson.  He certainly doesn't allow Scout or Jem to use racial slurs.  Another character that is imperative to this discussion would be Calpurnia.  Atticus regards Calpurnia as an equal.  She doles out wisdom and she mothers both Scout and Jem.  Atticus isn't afraid to stand up to people who disagree, either, ... such as Aunt Alexandra.  In this way, Calpurnia can be regarded as a very prominent member of the Finch family!  In fact, it is from this high perch that the children observe the very trial where Atticus tries desperately to symbolically defeat Jim Crow.

What role do the Jim Crow Laws play in To Kill a Mockingbird and how does Atticus' profession affect this?

Jim Crow laws played a significant role in the story and undoubtedly affected the outcome of the trial. Jim Crow laws were prejudicial pieces of legislation enacted in Southern states following the Reconstruction period that mandated racial segregation and discriminated against African Americans in nearly every aspect of life. Harper Lee's novel is set during the Jim Crow era, in which African Americans were considered second-class citizens and did not receive fair or just treatment under the law.

Unfortunately, Tom Robinson is a black man accused of assaulting and raping a white woman. In the racist town of Maycomb, which enforces and supports the prejudiced Jim Crow laws, Tom Robinson has no chance of winning the case. However, Atticus Finch plans to "jar the jury" by presenting the true facts of the case. Also, Atticus's children are young and naïve. They have faith that their father will win the case, but they do not take the racist nature of the jury into consideration or appreciate the extent of discrimination against African Americans in their community. One of the major themes of the novel examines the loss of childhood innocence. After witnessing Tom Robinson become a victim of racial injustice, the children's perspectives of their community changes. Overall, the prejudicial Jim Crow laws directly result in Tom Robinson's wrongful conviction and impact the children's childhood innocence.

Although Jim Crow Laws had a profound influence on the lives of most African-Americans in the South, it's difficult to say whether or not they are significant in To Kill a Mockingbird. It is clear that segregation has a strong influence on the white supremacist perspective of many white characters and their ability or willingness to believe that Tom is capable of having committed the crime. Atticus, Scout, and Jem, on the other hand, have more engagement with the African-American community through Cal and other members of the black community, which ostensibly influenced their slightly more liberal opinions of the black community in Maycomb.

As for the role of Jim Crow in Atticus' story, it is likely that it had little influence. Atticus is a man that is fiercely dedicated to upholding the equal application of the law, regardless of race. His decision to defend Tom, for example, is motivated by his belief that every person deserves fair and unbiased representation, as is stated in the Constitution. When it comes to the "separate but equal" lives that whites and blacks lead, he more or less accepts it as the way things are and doesn't let it influence his job as a defense attorney.

What excerpt in To Kill a Mockingbird responds to the Jim Crow laws?

One excerpt in the book that deals with the Jim Crow laws is Jem's explanation of Dolphus Raymond's family in Chapter 16. Jem explains to Scout that Dolphus Raymond has biracial children with his African American mistress and that the children are sad. Jem says: 

“They don’t belong anywhere. Colored folks won’t have 'em because they’re half white; white folks won’t have 'em cause they’re colored, so they’re just inbetweens, don’t belong anywhere."

Jem also tells Scout that Dolphus Raymond has sent some of his children up north, where they are more accepted. Jim Crow laws in the South meant that a person with any African American ancestry would be treated as a second-class citizen, and the rigid line between black and white left no room for other kinds of people.

In Chapter 19, Scout uses the logic of Jim Crow laws to explain why she feels that Tom Robinson is innocent. She says, "He seemed to be a respectable Negro, and a respectable Negro would never go up into somebody’s yard of his own volition." In other words, an African American person in Alabama had to know his or her place at that time; African American people would never venture into a white person's yard without being explicitly asked to do so because African Americans were well aware that they would be severely punished for doing so. There was a rigid color line, and Scout knows that Mayella Ewell must have invited Tom Robinson into her yard, as he wouldn't have gone without being asked. 

How does Atticus protest Jim Crow laws before Tom's trial in To Kill a Mockingbird?

Atticus Finch protests against Jim Crow by not allowing his children to refer to the African-American members of the community using the pejorative term that others do, and by treating Calpurnia as a member of his family.

In Chapter 9, when Scout comes home after Cecil Jacobs has made an announcement in the schoolyard that Atticus Finch defends n*****s, she asks her father if he does, and Atticus affirms that he defends them. But, he instructs Scout to not use this pejorative term for black people because it makes a person seem "common" (low class).

Then, in Chapter 14, after his sister Alexandra has come to stay with Atticus and his family, the brother and sister have an argument over Atticus's employment of Calpurnia. Aunt Alexandra tells Atticus that Calpurnia is no longer needed; however, in an "even" tone, Atticus replies,

"Alexandra, Calpurnia's not leaving this house until she wants to....She's a faithful member of this family and you'll simply have to accept things the way they are."

Atticus not only gives Calpurnia equal standing in his home, but he speaks of her as a family member. He praises her as being stricter with the children than a mother would have been, and argues that she raises the children with a sound set of ethics. Moreover, there is love shared among the children and Calpurnia. After Atticus's words, Alexandra is "furious" because her brother has gone against he conventional wisdom of their culture.