LOS ALAMOS — U.S. Energy Secretary Jennifer Granholm didn’t mince words when asked what led to her decision to restore J. Robert Oppenheimer’s national security clearance, 70 years after it was revoked.

Oppenheimer was railroaded, she told an audience of 600 gathered Friday at an auditorium on Los Alamos National Laboratory’s main campus.

She said he was punished for expressing misgivings about the increasingly destructive power of nuclear weapons, a politically unpopular stance at the time. Allegations he was a Communist sympathizer were just the rationale used to go after him, Granholm added.

Politics should play no part in personnel security, she said, echoing the written decree she issued in December when she reversed the 1954 decision by the Atomic Energy Commission to dissolve Oppenheimer’s clearance.

Erasing the unjust stain from Oppenheimer’s record is important, not only for his legacy but to help protect today’s scientists from being maligned and muzzled by those making politicized attacks on science, she said.

“We want scientists to openly question, and to openly speak up,” Granholm said, drawing loud applause.

Granholm expressed how being in Los Alamos was salient because it’s where Oppenheimer, the man whose name she posthumously cleared, launched the nuclear mission that carries on to the present.

She was part of a panel discussing the man known as the father of the atomic bomb after watching the lab-funded documentary Oppenheimer: Science, Mission, Legacy.

Other panel members were Charles Oppenheimer, grandson of the famous physicist; lab Director Thom Mason; Lisa Hruby, who heads the National Nuclear Security Administration; and Alan Carr, the lab’s senior historian.

They all agreed Christopher Nolan’s wildly successful movie Oppenheimer was renewing interest in the legendary physicist and generating more conversations about nuclear weapons.

Of course, it’s a dramatization, so it’s bound to bend some facts and embellish to enhance the narrative, Carr said.

That’s why documentaries are important to convey the facts, he added.

The lab’s 45-minute film delves into key points in Oppenheimer’s life story, from a preternaturally gifted but lonely child, to a rising young star blazing a luminous path in theoretical physics, to overseer of the Manhattan Project.

It segues into the tumultuous downfall that left him a devastated outcast from the military and academic world that, not long before, celebrated him. And finally it touches on his last days battling throat cancer before his death in 1967.

The film ties Oppenheimer’s pioneering efforts to the lab’s nuclear weapons research today, making the repeated point that LANL is building on the foundation he laid.

A few experts speaking in the film credit him with creating “big science” — a term denoting grander, more ambitious endeavors that go beyond current boundaries.

A faceless voice says it’s fair to call Oppenheimer the atomic bomb’s father — he didn’t build it singlehandedly, but he marshaled the forces that created it; being the orchestrater was part of his genius.

One of the film’s interviewees is Kai Bird, who co-authored American Prometheus, the Pulitzer-winning biography of Oppenheimer.

“He changed the world, but he gave us the weapons of mass destruction that could end the world,” Bird said, adding Oppenheimer was painfully aware of this.

In the film, author Jim Kunetka said when the first atomic bomb was detonated at the Trinity Site in Southern New Mexico, Oppenheimer clung to a pole shaking, both in fear of the test going horribly wrong and the ramifications of it succeeding.

Feeling the weight of the moment showed how human he was.

“Was he a hero?” Kunetka asked. “Yes, I think he deserves that title. But like all heroes throughout history, he was a flawed hero.”

The film doesn’t mention the devastation — both from the initial blast and later, radiation — inflicted by the two atomic bombs dropped on Japan.

Historians and nuclear advocates contend millions of lives were saved by ending the war without having to invade Japan.

Oppenheimer was elevated to celebrity status and flew high until the advent of the hydrogen bomb, when he began questioning the need for thermonuclear weapons.

His ambivalence incurred the wrath of hawks such as Lewis Strauss, who saw Oppenheimer’s influential voice in these matters as an impediment to ramping up America’s military might as Cold War tensions grew with the Soviet Union.

Granholm said the proceedings to determine whether Oppenheimer should lose his clearance were badly mishandled. Neither the scientist nor his attorneys were supplied with basic information — such as the specific accusations — so they could prepare a defense for the hearing.

Instead, Oppenheimer was blindsided and dragged through the mud, she said. His adversaries never showed he was disloyal, instead claiming he had too many character flaws to be privy to classified information.

Mason said Oppenheimer could have been stripped of his clearance simply for lying about his conversation with Haakan Chevalier.

Chevalier, a French literature professor, told Oppenheimer he’d heard there was a way to get technical information to the Russians. Oppenheimer failed to tell security agents about the exchange, and then later wouldn’t disclose Chevalier’s name because he was a friend.

His foes would use this against him later.

Mason said despite this serious misstep, he agrees with Granholm’s decision to restore Oppenheimer’s clearance because the process of stripping him of it was so flawed.

Charles Oppenheimer said he was grateful to Granholm for righting a long-ago wrong that marred his grandfather’s good name. His family never wanted to pursue a reversal of the 1954 decision, and instead chose to live with it, he said.

Now that the apology has been offered, it will be “unambiguously accepted,” he said.

“To forgive is divine,” Charles Oppenheimer said.