British author David Irving sued American Jewish historian Debra Lipstadt in 1996 for calling him, essentially, a Holocaust denier, resulting in the complex trial that serves as the basis for the film “Denial.” Lipstadt, played by Rachel Weisz, doesn’t mind defending herself, but the prospect of defending the Holocaust appalls her. “It’s not enough to say it happened,” says her own barrister, Richard Rampton (Tom Wilkinson). “How do we know it happened?” The question infuriates Lipstadt because, at that very moment, they are standing in a gas chamber at Auschwitz.

Topsy-turvy moments like that make “Denial” worth watching. Though its events took place 20 years ago, they have some relevance to our current election season which, as has become tradition, is marked by distorted facts, warped realities and furious table-thumping from all sides. Directed by Mick Jackson (“The Bodyguard”) from a screenplay by David Hare, “Denial” is a somewhat low-key courtroom drama that often feels merely interesting rather than consistently gripping, but it makes a strong case for the value of objective truth and clearheaded thinking.

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Much of the film’s tension comes from Lipstadt’s frustration with the British court system, where the burden of proof in this case lies with the accused, and her well-intentioned but somewhat smug defense team. Lipstadt wants to testify, but her lead lawyer, Anthony Julius (Andrew Scott), insists that’s a losing strategy. And so, this opinionated woman from Queens — Weisz doesn’t quite nail the accent — finds herself forced to clam up while others debate the topic to which she has devoted her career.

Irving makes for an only half-threatening villain. By 1996 he was already a fringe figure known for his ties to neo-Nazis, and his defamation suit against Lipstadt seems as self-destructive as the one Oscar Wilde launched against the marquess who accused him of homosexuality. Still, the great Timothy Spall brings Irving to life with malevolent eyes and a condescending grin. He’s so filled with hate that even the prospect of his own humiliation brings him joy.

“Denial” may not be entirely compelling, but its core ideas resonate. The film ably captures the sense of frustration — and fear — that arises when the truth goes up for grabs.