In his first term, President Trump signed an executive order directing federal agencies to defend the United States against an unusual type of nuclear strike that his advisers warned could shatter the power grid, wipe out critical infrastructure and lead to a national collapse.
Such an attack, caused by the detonation of a nuclear warhead miles above the earth, would not have the power to kill people directly. Instead, it could create an enormous surge of energy, known as an electromagnetic pulse or EMP, able to fry anything electrical on the ground below.
Detonated at the right height and location — say, 250 miles above Omaha — the impact might zap the computers of every modern car and airplane, trash the nation’s food supply, short out all telecommunications, do in the banking system and plunge the country into indeterminate darkness.
For more than a decade, a movement — largely among conservatives — raised awareness of such a threat, culminating in Mr. Trump’s 2019 executive order. Many of the most ardent voices in that movement are now members of the current administration, including Pete Hegseth, the defense secretary; JD Vance, the vice president; John Ratcliffe, the C.I.A. director; and Mike Huckabee, the U.S. ambassador to Israel.
Those very administration officials who long warned about EMP and tied it to an Iranian bomb also advised Mr. Trump on going to war with Iran.
But, strikingly, in eight months of conflict and many explanations about the reasons for attacking Iran, no official has publicly mentioned EMP or invoked it as a rationale.
The White House, when asked if the administration discussed the possibility of an Iranian EMP strike before launching the war, did not answer the question directly.
“President Trump will never allow Iran to pose a nuclear threat to the United States,” Anna Kelly, a White House spokeswoman, said in a statement. “The president will never allow a terrorist regime that has chanted ‘Death to America’ to harm our homeland.”
But for scientists and other experts, EMP poses a different question: Is the threat real?
National security experts often dismiss the EMP alarms as fearmongering. They consider such an attack unrealistic given that an aggressor would very likely face the prospect of deadly retaliation. And scientists caution that, while technically plausible, a successful attack would require not only a bomb far more advanced than what the Iranians appear to have been seeking, but also a precision detonation aligned with a tangle of environmental factors.
Newt Gingrich, a former House speaker and godfather of the EMP movement, scoffs at that kind of skepticism, having worked for decades to call public attention to the threat.
In an interview, Mr. Gingrich said the EMP activists were not alarmists but realists who understood that a single EMP bomb could instantly turn America into a wasteland.
When asked if Mr. Trump comprehended the pulse issue, Mr. Gingrich replied: “He understands.”
Frying Modern Life
As a phenomenon, EMP first materialized in 1962 when the U.S. military announced that it would, in the dead of night, high above the Pacific Ocean, detonate a hydrogen bomb. In Honolulu, hotels held rooftop parties so people could watch the test. Revelers filled parks and beaches, many prepared to toast the distant explosion. At zero hour, the sky lit up in surreal displays of reds, greens and blues.
Unexpectedly, the blast also shut down some of the city’s streetlights and power lines. The exact nature of the force was uncertain, because an East-West treaty soon banned the testing of nuclear arms in outer space. Overall, the nuclear effect remained more theoretical than experimental, more an odd possibility than a predictable certainty.
Nuclear experts came to see it as similar to a radio wave, only millions of times stronger. They found that any metal object — railroad tracks, pipes, aircraft bodies, power lines — could work like an antenna to pick up EMP energy and turn it into deadly currents.
Eventually, they determined that the electrical surges could fry not only delicate microcircuits, but by extension the whole technological infrastructure of modern life. No trains, planes or buses. No banks or credit cards. No lights, televisions or refrigerators. No running water.
Experts once believed that a crude EMP bomb was relatively easy to make. Any nuclear state with long-range missiles could loft one of its nuclear weapons to an altitude of anywhere between tens and hundreds of miles, set it off and generate a pulse. The higher the elevation, the wider its impact.
But Stephen M. Younger, a retired physicist who led bomb research at the Los Alamos weapons lab in New Mexico, said that an effective EMP attack required, at a minimum, the detonation of a hydrogen bomb. That held true for the American test over the Pacific. It might also explain why North Korea made no EMP threats during its atomic bomb tests and instead waited years until it had achieved the difficult step of making a hydrogen bomb, which can be thousands of times as strong as an atomic bomb.
A successful EMP attack requires both an unusually powerful bomb and the precise alignment of its gamma rays, which all nuclear arms emit. On Earth, they feed the fireball, helping to create the deadly force that shatters cities.
In the vacuum of space, however, the gamma rays create no shock waves or mushroom cloud. Instead, they strike the planet’s upper atmosphere, producing a chain reaction that creates something akin to a superstrong radio transmitter.
The gamma rays hit air molecules and knock out electrons that spin around the Earth’s geomagnetic field lines, creating waves of electromagnetic energy so powerful they can fry circuits thousands of miles away.
Atomic experts in the nation’s intelligence agencies have long kept a close watch on which countries have the ability to make and field that kind of weapon.
Building a Movement
Concerns about EMP spiked in 2008 after Iran was reported to have amassed a sufficient amount of enriched uranium to build an atomic bomb.
Those fears were supercharged by Henry Schwartz, a dairy entrepreneur in upstate New York whose business gave him the means, and whose pro-Israel politics gave him the motive, to start a movement.
In 2009, he founded EMPact America, an advocacy group that sought to ring EMP alarms. A single Iranian bomb, his team warned, posed an existential threat to both Israel and the United States.
His organization, on which he spent millions of dollars, would go on to play an outsize role in recruiting well-known conservatives to the cause. It would also help popularize the two main tenets of American EMP activists, which top scientists find baseless.
First, the group argued, a crude EMP weapon — that is, a rudimentary atomic bomb made by a rogue state or a terrorist group — would suffice to spark a devastating pulse. Second, the pulse would kill most Americans as the collapse of the nation’s power grid and supply chains led to a hellscape of riots and plagues, famines and vigilantes.
The eventual deaths, EMPact warned, could number up to 90 percent of the U.S. population, or more than 300 million people. That’s roughly four times the estimated number of individuals who died in World War II, the deadliest conflict in human history.
“Nine out of 10 Americans would be dead,” Frank Gaffney, a former Pentagon official, told EMPact’s first large gathering, held in 2009. Other speakers included Mr. Gingrich and Mr. Huckabee.
Julie Senko, a spokeswoman for Mr. Schwartz, 92, said he would be unavailable for comment.
In 2012, as President Obama began negotiations with Tehran to limit Iran’s nuclear program, Mr. Schwartz argued that a deal with Iran would further raise the risk of an EMP attack on America.
The United States “must act militarily to stop Iran,” Mr. Schwartz declared at a 2013 EMPact meeting in Washington, warning that an Iranian EMP strike would “end our civilization.”
At that meeting, John Bolton, a former U.N. ambassador, echoed Mr. Schwartz’s call for military action. He went on to serve as national security adviser in Mr. Trump’s first term and played a central role in drafting the EMP executive order.
In early 2014, David Bellavia, an Iraq war veteran newly appointed by Mr. Schwartz to run EMPact, joined forces with a fellow vet, Pete Hegseth. Together they publicized an EMPact meeting in Washington, titled “American Security and the Iranian Bomb.”
Mr. Hegseth, then a writer for The National Review, had already called for possible military action to “destroy the Iranian nuclear program.” A blog post he now wrote echoed the EMP activist view, warning that “even a crude” Iranian pulse weapon could bring the United States to its knees.
Over time, EMPact’s message reached federal lawmakers. John Ratcliffe, now director of the C.I.A. but then a Republican congressman from Texas, joined many of his House colleagues in late 2015 to push for improved protections of the electrical grid. EMP’s threat to health care, food supplies, and law and order, the legislators wrote, could lead to the “large scale loss of life.”
When the Republican Party adopted its national platform in 2016, it made the pulse threat a top issue. “EMP is no longer a theoretical concern,” the plank declared. It named Iran as a potential threat.
By the time Senator JD Vance became the Republican vice-presidential candidate in July 2024, EMP had morphed from a nerdy issue of specialists into a ubiquitous national security topic for a subset of U.S. conservatives.
Mr. Vance warned about the vulnerability of the grid’s transformers, as Mr. Schwartz and his team had years earlier. The giant devices, of which there are thousands, can stand more than two stories tall and weigh several hundred tons. Each raises and lowers voltages so electric power can race across the nation’s grid of overhead lines.
In October 2024, when Mr. Vance spoke on Joe Rogan’s podcast about the transformers, he conveyed some very bad news.
All the policy initiatives, notably Mr. Trump’s EMP executive order, as well as state, federal and private plans meant to strengthen grid protections, had essentially come to naught. The nation, Mr. Vance observed, had few, if any, backup transformers to replace the ones that an invisible burst of EMP energy would knock out.
“It’s actually a scandal,” he said.
Later in the show, he called Iran “the biggest foreign policy threat that we face in the Middle East.”
More Difficult Than It Sounds
Despite the waves of public alarms, nuclear scientists who study EMP describe the ranks of activists as lost in a fog of physical impossibilities.
“The kind of bomb that Iran could make is not going to shut down all communications,” said Dr. Younger, the Los Alamos physicist. “It’s not going to shut down the power grid.”
In an interview, he said that an attempted EMP strike would have an even more basic drawback: The pulse by nature is stochastic, a scientific term meaning random. That volatility, Dr. Younger added, undermined its military utility.
“Sometimes it produces an effect and sometimes it doesn’t,” he said. “One of the downsides for EMP as a weapon is that you can’t depend on it.” Experts put the odds of success, even for a highly accomplished nuclear state, as equal to a coin flip.
An EMP attacker who nonetheless sought to maximize the chances of a success would need information from the networks of satellites and ground stations that monitor the planet’s space weather, which fluctuates on scales ranging from seconds and minutes to days, years and decades. As regular viewers of the night sky know, such changes in the near-Earth environment can send the shimmering lights of the aurora borealis far south.
Countries such as Iran and North Korea have little access to such information in real time, unlike the United States, China and other developed nations, which closely track space weather, in part because radiation spikes can endanger satellites and astronauts.
More specifically, the known variables that can foil an EMP attack include insufficient blast height and poor alignment of the exploding weapon with the Earth’s geomagnetic field lines, as well as solar winds, flares and storms.
Other variables, experts say, are classified, like many aspects of nuclear weapon design and use.
“EMP has become a cottage industry,” said Dr. Younger, who once directed the Defense Threat Reduction Agency, an arm of the Pentagon that seeks to counter weapons of mass destruction.
“There’s money to be made by scaring people in Washington,” he added. “That’s how it works. Is EMP possible? Yes, it is. Do we need to be careful? Yes, we do.”
But Dr. Younger said that, on the list of existential threats to the United States, a successful Iranian EMP attack ranked so low as to warrant little, if any, attention.
“It’s extraordinarily unlikely,” he said.
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