In Taxi Driver, Travis Bickle ruins his relationship with the woman he likes. Then, he tries to get her back, fails, starts becoming angry, fantasizing with killing people. Part of his hatred is against the scum of society (pimps, whores, druggies, etc, which we see from his conversation with the Senator), but another is against the Senator.
Why does he try to assassinate him?
In Quora, they talk about
- Political reasons - right wing VS left wing, but Travis doesn't know much about politics and does not seem racist, so why would this matter to him? Also, their explanation is mostly out-of-universe:
Travis Bickle's attempted assassination of Senator Palantine is like a mirror image of Bremer's assassination attempt against Wallace
- Jealousy - Travis would be a lot more jealous of her friend Tom, whom he already said he disliked, than the Senator which does not seem to have any direct contact with her, as far as Travis knows
Travis may perceive Palantine as a sexual rival to him for the affections of Betsy
- Director ambiguity - again, an out-of-universe explanation
Martin Scorsese has a tendency to make movies with ambiguous endings that show a great deal of ambivalence about fame
What are the in-universe reasons for Travis to try to assassinate the Senator?