You don't really know Travis Bickle's origin story, but there are a few things we can surmise. Unlike Robert De Niro, the actor who played him, he wasn't born and raised in New York, but rather came there later in life. He claims to have been an ex-marine, but he may also have been involved in right-wing militia or hate groups. He's probably a virgin. He currently avoids any hard drugs, but it's possible he used hallucinogens in the past.
He moves in a world of surfaces. The black people of New York are only scum to him. Palatine, the presidential candidate is a fake spewer of platitudes. He is no different as a taxi cab passenger than he is as an image on television. Bickle lacks any aesthetic interests, beyond his two romantic interests, Betsy, the prim Madonna he wishes to violate, and Iris, a 12-year-old prostitute he wishes to rescue. Scorsese's camera may discover the ugly beauty in the crime-ridden, impoverished New York on the brink, but Travis Bickle can't access any of it. The only movies that interest him describe the sexual experiences he will never know. He doesn't care for music or dancing.
His closest friend is Wizard, who is at best a hapless uncle who reaches out, but only so much, to a lost nephew.
When he finally kills, he experiences the equivalent of an orgasm and then peace.
He is a lonely man who knows he is lonely, and who tries to be a "person like other people." For a psychopath, he has striking fits of self-awareness.
Travis Bickle may be a product of the post-Vietnam, post-Watergate insanity, but today, it's impossible to read Taxi Driver without thinking of mass shootings, our increasingly insane gun culture, and racial paranoia. Travis Bickle would have hated Obama with far more rage than he ever could have hated Palantine.
Is Donald Trump -- a junk-food addict, a man who lacks internality, a monster who spews hatred but wouldn't know what to do with a gun -- as De Niro has recently said, Travis Bickle? Maybe not. But Travis Bickle's descendants make up a good part of his base.