The couple are separated and haven't spoken for three years. The film suggests that Travis' violent and jealous nature led to the marriage's dissolution and that Travis held more right winged ideals whereby the male is the provider and the head of the family. When he fails at this, his behavior turns aggressive reflecting cultural generalization in America.
Men have trouble communicating so they turn their frustration into negative behavior.
Conversely, his wife represents a woman with liberal values suggested by the fact that she left him, and their son, to find a better life for herself. She entrusted her young son to the care of Travis' brother wife and ends up working in a type of sex club. Formerly in a subordinate role to her husband working there represents her attempt to reclaim some sort of power. At the same time, she falls into the cultural generalization that a woman who has left her family is only able to support herself by working in a profession that exploits women. The film, I think, shows that these two characters are trapped in a world governed by Republican values.