I was never clear on how that fit in with his other obsessions, not even his obsession with Betsy.
Bickle feels marginalized and wants to do something important. Loneliness has followed me my whole life. Everywhere. In bars, in cars, sidewalks, stores, everywhere. There’s no escape. I’m God’s lonely man… June 8th. My life has taken another turn again. The days can go on with regularity over and over, one day indistinguishable from the next. A long continuous chain. Then suddenly, there is a change.
and later,
*Listen, you fuckers, you screwheads. Here is a man who would not take it anymore. A man who stood up against the scum, the cunts, the dogs, the filth, the shit. Here is a man who stood up. *
Bickle thinks that by doing something dramatic, something heroic, that he’ll attract attention, connect with other people, and impress Betsy, as he does in his final dying hallucination. No, it doesn’t make a lot of sense; Bickle isn’t reasonable or sane.
Stranger
It made about as much sense as the shooting of Giffords. Or Reagan, or Lennon.
Unbalanced people focus their obsessions on famous people who they think wronged them, or just stand out enough when one wants to make a statement.
In this fictional case you could conclude also that Palantine was an object of resentment because Bickle was rejected by the candidate’s campaign workers.