U.S. President Donald Trump signed a new executive order on Tuesday, mandating a government-wide effort to harden critical elements of the nation’s infrastructure against the possibility of an electromagnetic pulse (EMP) attack.

Put simply, an electromagnetic pulse is a short burst of a specific kind of radiation that’s most commonly released by a nuclear detonation. EMPs represent a particularly significant threat to the United States from nations with underdeveloped nuclear programs such as North Korea and Iran, as the weapon doesn’t need a particularly hardened reentry vehicle in order to function. Instead, the nuclear warhead is detonated high above the target area in low earth orbit.

Electromagnetic radiation comes in three types of pulses (commonly called E1, E2, and E3) that effect everything within line of sight of the blast, overloading electronic devices, disrupting the flow of electricity, and generally throwing the affected area back into the Stone Age.

The Washington Examiner quoted EMP expert Dr. Peter Vincent Pry, author of the report “Nuclear EMP Attack Scenarios and Combined-Arms Cyber Warfare.” In it, Pry details the devastation of an EMP attack.

Everything is in blackout and nothing works. The EMP sparks widespread fires, explosions, all kinds of industrial accidents. Firestorms rage in cities and forests. Toxic clouds pollute the air and chemical spills poison already polluted lakes and rivers.

In seven days, the over 100 nuclear power reactors run out of emergency power and go Fukushima, spreading radioactive plumes over the most populous half of the United States. There is not even any drinking water and the national food supply in regional warehouses begins to spoil in three days. There was only enough food to feed 320 million people for 30 days anyway.”

EMP Threat: North Korea suggests 'atmospheric' detonation over the Pacific for next nuke test

Read Next: EMP Threat: North Korea suggests 'atmospheric' detonation over the Pacific for next nuke test

It’s hard to overstate the potential damage a large-scale EMP attack would cause. According to Pry’s report—recently declassified by the now defunct Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack—a nationwide blackout could lead to the deaths of 90 percent of the nation’s population.

Although it is very difficult to predict exactly which electronic systems would be upset, damaged, or destroyed by an EMP attack, with certainty massive disruption and damage will be inflicted on unprotected electronics within the EMP field and, because of cascading failures, far beyond. EMP is analogous to carpet bombing or an artillery barrage that causes massive random damage that is specifically difficult to predict, but reliably catastrophic in its macro-effects.”

Trump’s new executive order hopes to curb the destructive capability of such an attack. The order is the first of its kind, calling on federal agencies to work to identify EMP threats to vital elements of the nation’s infrastructure, and devise ways to harden those systems or otherwise protect them against such an electromagnetic attack.

“It is the policy of the United States to prepare for the effects of EMPs through targeted approaches that coordinate whole-of-government activities and encourage private-sector engagement,” the executive order states. The order mandates the federal government to devise ways to spot incoming EMP attacks and warn the populace, protect the populace against the effects of the attack, respond to an attack, and finally, to recover from it.

“President Trump will always do what it takes to keep Americans safe. Today’s executive order— the first ever to establish a comprehensive policy to improve resilience to EMPs—is one more example of how the administration is keeping its promise to always be vigilant against present dangers and future threats,” said White House Press Secretary Sarah Sanders.

Destructive EMPs are also caused by naturally-occurring phenomena, such as solar flares. Protections against man-made attacks would work against similar natural disasters.