Last year was an apt one for the 40th anniversary of Taxi Driver, since in many ways Travis Bickle embodies the collective psyche of Trump supporters. A simplistic sense of political disenfranchisement, innate racism, fondness for firearms, self-destructive impulses; all of these seem to be echoed in the way Americans voted, or – perhaps more correctly – the way Trump stoked the “inner Travis” that lay dormant. One might equate Trump’s hate-fuelled policies with the famous line screenwriter Paul Schrader gives the embittered Travis: “Some day a real rain will come and wash all this scum off the streets.”

The film’s canonical status and longevity is understandable. The convergence of Scorsese, De Niro and Schrader, each of them on fire creatively at this early stage in their careers, was a fortuitous alignment. Scorsese’s visionary film-making has been much celebrated. The nausea-inducing yellow of the cab emerging out of the steam of the New York streets; the vertiginous descent into the fizzing glass of Alka-Seltzer in the diner; the God’s-eye view of the blood-drenched finale – all of these are etched into the audience’s subconscious, the intensely subjective directorial choices keeping us locked into Travis’s warped perception of the world.

Suppressed sociopathic rage … Travis Bickle. Photograph: Allstar/Cinetext/Columbia

As Travis, De Niro inhabits a role almost completely devoid of psychological detail or backstory. All the usual points of entry for understanding a character are denied us, yet his performance is hypnotic. Travis simultaneously repels and attracts: the suppressed sociopathic rage of his voiceover is repulsive, while at the same time his hopeless inarticulacy in “real” life (as when he tries to open up to Peter Boyle’s fellow cabbie Wizard) acutely exposes his vulnerability and innocence. This mix is perfectly encapsulated by his horribly ill-judged decision to take Betsy (Cybill Shepherd) to a porn flick on their first date. There’s a wild disparity between his voiceover and what we actually see him doing, proclaiming his commitment to staying in shape (“You’re only as … healthy … as … you … feel … ”) while necking handfuls of pills. As Schrader himself noted: “The character I wrote was going crazy in a more linear fashion than the character Bobby acted; his characterisation zigs and zags.”

Schrader’s screenplay was profoundly confessional. When film critic Pauline Kael asked him about the inspiration for Travis, he replied: “It’s me, without any brains.” Schrader had experienced something of an existential crisis prior to writing Taxi Driver. He was recently divorced, drinking heavily and sleeping in his car. When he was hospitalised with a stomach ulcer, the image of the cab driver struck him. “The man who moves through the city like a rat through the sewer; the man who is constantly surrounded by people, yet has no friends. The absolute symbol of urban loneliness. That’s the thing I’d been living; that was my symbol, my metaphor.” Schrader’s spiritual state remained troubled as he worked on the script. According to legend, he wore a brass crown of thorns while writing, with a gun on the desk next to the typewriter to deter writer’s block.

In retrospect, Schrader has spoken of the film as “juvenilia … an adolescent, immature mind struggling to identify itself”, and indeed, next to the classically handsome specimens of 70s American movie-making – Godfathers I and II, Nashville, The Last Picture Show, Annie Hall, Chinatown, The Deer Hunter, Apocalypse Now, to name a few – Taxi Driver is a strange, awkward film: a gangly, acne-faced teenager skulking in the shadows, fixing us with a piercing stare.

Taxi Driver’s blood-drenched finale. Photograph: Ronald Grant Archive

This awkwardness stems from the two diametrically opposed aesthetic and philosophical attitudes that coexist in it. On the one hand there is a European existential influence, particularly as manifested in Robert Bresson’s works. Taxi Driver is peppered with nods to the French film-maker: Travis’s diet of bread soaked in peach brandy, for instance, echoes Diary of a Country Priest, whose protagonist subsists solely on the Eucharist, the bread soaked in wine used in Holy Communion. Travis also worries that he has stomach cancer, the disease from which the priest in Bresson’s film dies. Films such as Country Priest, Pickpocket and A Man Escaped insist on a spiritual interpretation by employing a visual and narrative asceticism, an abstinence from the usual sensuous cinematic pleasures; instead they try to promote in the audience a state of mystical or religious contemplation that will prepare them for the final revelatory moment of transcendental grace.

No less concerned with Travis’s spiritual predicament, Scorsese’s approach could not be more contrary: ecstatic and immersive, he utilises all the medium has to offer to heighten the subjective perception of his protagonist. Filtering the story through such a powerful vision works against the proselytising of Schrader’s existential model, and the ending – the sudden, paranoid flicker in Travis’s eyes seen in the rear-view mirror – negates any hope of transcendental grace.

Taxi Driver has a unique power to devastate and obsess. No wonder it appeals to teenagers going through the profound awkwardness of adolescence: the film’s aesthetic fragmentation perfectly mirrors all the contradictory emotions and conflicting thoughts that arise when one begins to truly comprehend the adult world, with all its flaws.