An essay written in an examination period for a Shakespeare class. The topic "Challenging the law" was given as the starting point.
Challenging the law seems to be best taken in the sense of challenging "fundamental" law. A trial of a person for a crime is not in this sense a challenge of the law. Rather, a challenge of the law entails one seeking to refute or challenge basic or specific laws.
Bollingbroke makes at least two such challenges, which are related i.e. the second is not possible without the first. Compression of time in the play suggests Bollingbroke had a military force, although this is never tested before his exile. His first challenge (or defiance) of the law comes when he denies Richard' authority and returns from exile. Richard's inability to uphold his "lawful" claims on Bollingbroke's land and his exile make Bollingbroke's challenge successful.
Bollingbroke's second challenge is in some ways more lofty. However, it is not a new challenge. This is, Bollingbroke challenges the law(s) of inheritance of the crown and usurps it from Richard. While the "God given" laws on descent of the crown seem loftier and therefore harder to challenge, Richard himself had successfully these laws so Bollingbroke knew that it could be done.