(Michael Crowley)  In October of 2004, Vice President Dick Cheney issued one of his regular dire warnings that terrorists could use a weapon of mass destruction, including a nuclear bomb, to kill thousands of Americans. “You have to get your mind around that concept,” Cheney said.

One person who didn’t need persuading was Ashton Carter, President Barack Obama’s nominee for secretary of defense. Three years after Cheney’s comment, Carter co-authored a policy paper titled: “The Day After: Action Following a Nuclear Blast in an American City.”

The disturbing essay was the stuff of a Hollywood techno-thriller. It recommended closing highways to panicked survivors so emergency responders could race to the scene. It imagined mass evacuations of other cities — “[i]f one nuclear weapon goes off, more are likely to follow”— and the prospect of negotiating with the terrorists to prevent more mushroom clouds. It floated the idea of setting up an emergency, extra-constitutional governing body advised by the chief justice of the United States.

“As grim a prospect as this scenario is for policymakers to contemplate,” Carter wrote, along with two co-authors, they have no other choice.

Though Carter may not always share Cheney’s hawkish views, both men have long been drawn to thinking about the unthinkable. As a young Pentagon official in the mid-1990s, Carter fixated on the danger of an accidental nuclear war, fighting — and badly losing — a bureaucratic battle to reduce that terrifying prospect. Later he turned to the threat of catastrophic terrorism and its potential effects on American society years before Sept. 11. More recently, he has fretted about the effect of invisible gamma rays on crucial electronics.

He’s the Democrats’ Dr. Doom. In recent years, Carter, who has a Ph.D. in nuclear physics, has broadly diversified his portfolio to include relatively mundane topics like weapons acquisitions and budget reform. But if confirmed as secretary of defense, he would bring to the job an unprecedented expertise in epic disaster.

“These are issues that he has wrestled with for his whole career,” said Graham Allison, director of the Belfer Center for Science and International Affairs at Harvard University’s Kennedy School of Government and a friend of Carter. “With all of the noise about all of the issues on the agenda you lose sight that there are [threats] a whole lot worse than what’s happening in the Ukraine, or with ISIS, or whatever.”

Some close observers call Carter’s doomsday preoccupations a natural outgrowth of his background. “I think it has a lot to do with his grounding in science, which tends to put him on the forward edge of threats facing the U.S.,” said a former aide to Carter. “Things that might sound almost sci-fi to your average policy wonk are real and tangible to him.”

As a result, Carter is likely to weigh in forcefully with Obama on threats such as mass-casualty terrorism and nuclear proliferation. In 2006 he publicly urged President George W. Bush to consider a surgical strike on a North Korean missile platform before that country could test an intercontinental missile that might one day be fitted with a warhead that could target America. (“It undoubtedly carries risk,” Carter wrote, along with former Defense Secretary William J. Perry. “But the risk of continuing inaction in the face of North Korea’s race to threaten this country would be greater.”)

In testimony before the Senate Armed Services committee last week, the 60-year-old Carter mostly stuck to administration talking points on familiar challenges like Iran, Ukraine and the extremist group known as Islamic State in Iraq and the Levant. He also struck a sunnier note than some of his disaster writings, saying that American strength “makes me proud and hopeful, and determined to grab hold of the bright opportunities in front of us as well as to counter the very real dangers we face.” He is expected to be confirmed easily later this month.

Still, some critics worry about the implications of Carter’s doomsday expertise. “He has a little bit of a fixation on the 1 percent threat, if you will,” said Michael Cohen, a fellow at the Century Foundation. During the Bush White House years, Cheney argued that threats with potentially disastrous consequences — but a probability as low as 1 percent — had to be treated as likely. “Cheney is very much of the same mindset,” Cohen said, adding that such thinking exaggerates danger and warps policy and budget priorities.

Carter was fluent in the language of destruction from early in his career. In 1984, when he was just 30 years old, he co-edited and contributed to a book on missile defense — then widely known as “Star Wars” — in which he wrote in bloodless prose about mass death. “The density of people in an urban area, and hence the computed fatalities [from a nuclear blast] changes with time as they commute between home and work or leave for holiday weekends,” Carter wrote, adding that “more than one weapon may be necessary to destroy a city completely.”

After the Soviet Union’s 1991 collapse dramatically reduced the threat of nuclear war, allowing most Americans to breathe a sigh of existential relief, Carter focused on a new nightmare: an accidental nuclear holocaust.

As a midlevel Pentagon official in the Clinton administration, Carter argued in a 1994 policy review that having a massive nuclear arsenal on hair-trigger alert created more risk than security. He fought to slash America’s nuclear stockpile and to restrict the president’s ability to launch intercontinental missiles on a few minutes’ notice. That posture, Carter argued, risked a misjudgment under pressure or an accidental launch that would kill tens of millions.

The military brass had little interest in the young wonk’s bold ideas, which were quashed by generals who, as one policy review participant later told the author Janne E. Nolan, “hopelessly outmatched Carter in the art of bureaucracy.” (By all accounts, he has since become a master bureaucratic operator.) His ideas were not implemented, and he has shown no sign of pressing them as secretary of defense.

During his testimony last week, Carter repeated several times that he is “a strong believer in a safe, secure and reliable nuclear arsenal,” but offered few other details.

Carter had more success in the mid-1990s implementing a Pentagon-led program to remove nuclear weapons and material from former Soviet republics. In his Pentagon office, he proudly displayed a photograph of a disarmed Ukrainian SS-24 missile in its silo, a tangle of exposed wires where its warhead had been.

“I always point to this picture,” Carter told this reporter at the time, “and I like to say that if you compare this to Somalia, to Haiti, to Bosnia — all of the things that have so preoccupied the public during the [Clinton years], they’re not nearly as important to our security as this.”

As such programs advanced and the Russian threat receded, Carter began to focus on terrorists empowered by dangerous technology. Years before the Sept. 11 attacks, Carter — then an academic at Harvard — warned that U.S. policy makers did not fully grasp the threat of a major terror attack inside the country.

“Long part of the Hollywood and Tom Clancy repertory of nightmarish scenarios, catastrophic terrorism has moved from far-fetched horror to a contingency that could happen next month,” Carter wrote, with two co-authors, in a 1998 Foreign Affairs article flagged by POLITICO’s Morning Defense in December. Carter and his co-authors presciently warned that the U.S. government might respond by “scaling back civil liberties, allowing wider surveillance of citizens, detention of suspects, and use of deadly force,” and urged policymakers to better prepare.

Among other things, the article called for creation of a “National Terrorism Intelligence Center” that sounds much like the National Counterterrorism Center that is now a crucial part of post-Sept. 11 homeland security.

Not only did the Sept. 11, 2001, attacks prove Carter’s fears justified, they further concentrated his mind and he began to explore the possibility of nuclear terrorism in more detail. He even helped organize mock exercises simulating an atomic blast, including one involving a city in California, according to one participant.

When he returned to the Pentagon under Obama in 2009, Carter spent much of his time on more traditional issues like the budget and weapons programs. But he also kept his mind on Hollywood-style horrors.

One is the threat of electromagnetic pulse. The phrase describes an invisible burst of gamma rays produced by nuclear explosions that can permanently fry electrical circuitry. Some experts and officials warn that one strategically placed high-altitude nuclear explosion could destroy America’s power grid, producing apocalyptic conditions nationwide. Cheney is among them. “It would literally shut down our civilization,” the former vice president said on Sean Hannity’s radio show last year.

Many nonspecialists ridiculed such talk. But as undersecretary of defense in 2010, Carter ordered a task force to study the ability of Pentagon systems to withstand EMP.

None of this makes Carter a trigger-happy hawk, say his allies. Allison describes him as an “evidence-based” pragmatist.

“He’s not alarmist,” says Allison. It’s just that Carter is more attuned to dangers “that may seem like science fiction to folks who are just captivated by today’s news. What’s current is not necessarily what’s most important.”