Explain how the Great Gatsby is political on some level. Specifically, how the author addresses the issues of selfishness, class (and the large gap between upper and lower classes), and a general lack of morality in society
The mention of bootlegging and the criminal element involved alludes to the mistake of the 18th Amendment which brought great profits to organized crime and the likes of Meyer Wolfscheim. Also, in The Great Gatsby in Chapter One, the supercilious Tom Buchanan alludes to Lothrop Stoddard's book, there is a political innuendo on the part of F. Scott Fitzgerald who was himself a liberal and disapproved of Stoddard's writings.
To make this connection, we need to use a rather loose definition of "political", but, with that said, there is certainly plenty of commentary offered in Gatsby regarding social values.
I don't know that a lack of morality at large in the society depicted qualifies even loosely as a political issue, as morality is inherently and finally individually defined, but I might be persuaded to posit that the generic role expectations that drive these characters to do what they do can be seen as political.
Tom's treatment of Wilson is personal, not political. The same goes for the various affairs between Daisy and Gatsby and Tom and Myrtle. What is, ironically, impersonal is Daisy's choice to marry and stay with Tom.
My focus goes first to Daisy as an example of a character who is dominated by outward and accepted social mores. She refuses to divorce Tom, though she knows he is cheating, because divorcing him would mean giving up on the image they have created together.
She marries Tom in the first place because she feels pressure to fulfill the expectations placed on her by society. Daisy cannot wait for Gatsby to return from the war because the pressure on her is too great for her to withstand. Granted, Daisy is not particularly strong or willful when it comes to standing against perceived social pressure. But this is the point.
To a large degree Daisy's decisions are driven, not by love or emotion, but by her perceptions as to what her community expects her to do. She is dedicated to maintaining the trappings of success, which for her do function as a trap.
The reason we might see Daisy as a character influenced by politics is that her perceptions of the pressures on her are purely impersonal and related to shared, abstract views of gender and success.