Twice in the last month, the President of the United States has claimed that the Pentagon has weapons even more powerful than nuclear weapons, with the ability to easily kill millions. He is either bluffing, confused, or is incapable of understanding the difference between conventional and nuclear weapons.

President Donald Trump made the claim during remarks to commemorate the 18th anniversary of the September 11th attacks in New York, Washington, and Pennsylvania.

, Trump told an audience, emphasis mine:

“The last four days, we have hit our enemy harder than they have ever been hit before, and that will continue,” Trump said, apparently referring to the Afghanistan war and drawing applause from the crowd. “And if for any reason they come back to our country, we will go wherever they are

Less than a month ago, on August 20, Trump that the U.S. military could kill 10 million people in Afghanistan within a week. “This is not using nuclear [weapons],” he said.

So what could he be talking about, then?

One possibility is that he thinks the United States could drop so many conventional weapons they would have effects greater than nuclear weapons. The second possibility is that he’s talking about a new type of weapon, one previously limited to science fiction.

Conventional weapons—and let’s just limit our discussion to blast weapons—use high explosive weapons to deal damage through overpressure, heat, and shrapnel. Examples of these are aircraft bombs, which typically range from 250 to 2,000 pounds (one ton)—mostly high explosive with a steel bomb casing. Tomahawk cruise missiles and similar weapons have 1,000 pound high explosive warheads. These are the weapons that would do the most damage, quickly.

There are exceptions. A few outlying bombs, such as the Air Forces’s , also known as the “Mother of all Bombs,” get up to 21,600 pounds. Russia’s , which it calls the “Father of all Bombs” reportedly has a yield of 44 tons. But these are specialized bombs, and few and far between.

The point is, conventional bombs typically max out at one ton, and often rate far less. In fact, thanks to precision targeting, the long term trend is toward increasingly smaller warheads in exchange for longer range and improved ability to penetrate hardened structures, like a command bunker.

Nuclear weapons, on the other hand, are easily a thousand times more powerful than conventional weapons. The first atomic bomb used in action at Hiroshima had an explosive yield of 16 kilotons—or 16,000 tons of TNT. That’s the equivalent of 16,000 Mk. 84 2000 pound high explosive bombs. A B-52H bomber can carry just 18 Mk. 84 bombs, meaning it would need to fly 888 missions to drop the same amount of TNT as the Hiroshima bomb. Other bombers and fighters could pitch in to help out, but the point is it would take hundreds of missions over several days just to replicate Hiroshima.

Another thing to consider: U.S. nuclear weapons are now considerably larger and more destructive than those used in World War II. The on America’s Trident missile submarines is rated at 100 kilotons—about six times bigger than Hiroshima. The on the Minuteman III missile is 300 kilotons, the ranges between 100 and 150 kilotons, and the has a staggering yield of 1.2 megatons (1,200 kilotons.)

Conventional bombs, even served up in large numbers, could not approach the destructive power of nuclear weapons. The 44-ton “Father of All Bombs” looks like a wet firecracker compared to the 1,200,000 ton B83 bomb. Even the United States, which virtually invented assembly line warfare, could not build enough cruise missiles, bombers, and bombs to outdo nuclear weapons.

Could Trump be talking about something else? Whatever the weapon, it would have to use even more of a compact energy source than a nuclear bomb for it to be more powerful.

Antimatter bombs fit the bill: just one pound of antimatter would generate an explosion . A pound of plutonium, by comparison, of nuclear boom.

In 2004, The San Francisco Chronicle the U.S. Air Force was researching antimatter bombs. The Chronicle reported that in March 2004, , director of Revolutionary Munitions at in Florida, gave a speech on the usefulness of antimatter as an explosive. A copy of Edwards’ speech posted on the Internet at the time emphasize the lack of radioactivity of an antimatter bomb explosion versus a nuclear bomb explosion. After the Chronicle began making inquiries, the Air Force clammed up about an antimatter bomb and nothing I can find has been written about it since.

Still, is there an antimatter bomb be out there, in some black Pentagon program? Probably not. Anything more than a token amount of antimatter is out of reach for a long, long time.

Scientists believe that it would take ” just to accumulate a gram’s worth of the stuff—all that time and money for an explosion less than half the size of the W76 warhead. Until it becomes much, much easier and cheaper to acquire antimatter, such bombs are a dead end. For now antimatter bombs .

And so either Trump is bragging about a superweapon that doesn’t exist or he apparently has no idea how powerful nuclear weapons are. I’m not sure what’s dumber, or scarier.