Baltimore, 1974. Sam Bicke explains and explains and explains. He has solved everything, why he is right and the world is wrong, and he has a strong obsession with injustice. “My name is Sam Bicke,” he said at the beginning of one of the tapes he sent to Leonard Bernstein, “and I consider myself a grain of sand.” He sells office supplies, really bad. The marriage is over. The bank does not act on the loan application. Nixon is still at the White House. The Black Panthers are being persecuted. It was all part of the same anger churning within him.

Sean Penn plays Bicke as a man who has always been socially incompetent and now, when his life falls apart, goes insane. His own frustrations and the evils of the world are all the same, somehow someone else’s fault, and in the opening scene of “The Assassination of Richard Nixon,” we see him in an airport parking garage, hiding a gun in a leg brace. . He sent one last tape to Leonard Bernstein. He plans to hijack a plane and fly it to the White House.

There’s the original Sam Bicke (spelled Byck), whose plan of course fails. Niels Mueller’s film is based on his failed assassination scheme, but many other details, including some scathing humorous scenes, are the inventions of Mueller and his co-writer, Kevin Kennedy. It’s a character study of a marginal man off the rails, and Penn is brilliant at evoking how everyday life itself is filled, for Bicke, with countless challenges to the rigidity of right and wrong.

Consider his job as an office supply salesman. He sells chairs covered in Naugahyde. The client asks if it is leather. He said they didn’t. Her boss, Jack Jones (Jack Thompson), walks in and smoothly explains that they are “Naugahyde-coated skin.” Uh huh. When Sam offers a client a discount to close the sale, Jack calls him into his office and yells at him for selling the table at a loss. The client hears. Then Sam found out that the joke was on him. Jack wants to help him, and recommends reading The Power of Positive Thinking, and How to Win Friends and Influence People.

His sense of honesty offended by his work, Sam becomes obsessed with Nixon. “He made us a promise — he didn’t keep it. Then he sold us on the exact same promise and he was re-elected.” He visits the local Black Panther office to make a donation, and as a Panther official (Mykelti Williamson) listens in disbelief, shares his ideas about renaming the Panther to Zebra and accepting white members — like Sam Bicke, for example.

He dreams of saving his marriage. He couldn’t make her understand it was over. She is presented with divorce papers and protests, “we should have worked this out!” In one of the film’s most painful moments, he talks to the family dog: “You love me, don’t you?” The dog seems indifferent.

Simmons (Don Cheadle). It depends on the loan. Sam and Bonny were a bad risk, the Small Business Administration issued a paperwork, and Sam explained and explained how important the loan was, and how urgent it was that it came quickly.

Penn conveys anger through the small details it contains. He is one of our great actors, able to invest unimportant characters with importance because their lives are so pressing for themselves. Was it Penn or the filmmakers who thought of a twist where Sam wears a fake mustache in an airport parking lot. What for? No one knows who he is or what he looks like, and if his plan works, there will be no more Sam Bicke, mustache or not.

Penn points out he’s always on the outside. Away from his house. Rejected by the bank. Does not qualify for Black Panthers. Outsiders in the office, listening to his boss and coworkers laughing at him. The only person he could trust was Leonard Bernstein, whose music he admired. (The original Bernstein, who received the cassette from the original Byck, was confused to attach any distance to the piracy plot.)

“The Assassination of Richard Nixon” is about a man on a collision course; given the firm terms in which he set right and wrong, sooner or later he would crack. He has no clue about proper behavior, about how others perceive him, about what may be right but still isn’t. The film’s title has one effect before we see it, and another after, when we can see the greatness and self-deception implied in it. What really happened was that Sam Bicke killed himself.

Does the film have a message? I don’t think it wants it. It’s about a man’s journey to madness. A film can be a character study, like this one. That is enough. A message may seem vague and haphazard. Of course our opinion of Nixon, Vietnam, and the Black Panthers is irrelevant; they enter the film only as objects of Bicke’s obsession. We can’t help but feel a connection to another would-be assassin from the 1970s, another obsessed loner, Travis Bickle. Travis wrote his thoughts in a journal; Sam uses a cassette. They feel the need to justify themselves, and don’t even have an audience.