Trump has long promised a 'beautiful' wall. Now he's pledging 'the greatest dome ever.'

MANCHESTER, N.H. — After breezing through his usual lines about wanting to build a border wall and to “drill baby, drill” for oil, former President Donald Trump has been adding a new refrain to his speeches — a promise to build something like Israel’s Iron Dome, but better and over the entire U.S.

“We’ll build an Iron Dome over our country, a state-of-the-art missile defense shield, and it’s all made in the USA,” Trump said Sunday at a rally in New Hampshire. “I think it’s time that we have one.”

“I will prevent World War III. We’ve never been so close. You just have to check out the news. And we will build an Iron Dome over our country — a state-of-the-art missile defense shield,” he said here Saturday.

“It’s a very big deal for me,” he said of the idea last month in Iowa. “We’re giving billions of dollars to other countries so they can build a dome. But we don’t have a dome ourselves. We’re going to have the greatest dome ever.”

The Israeli missile defense system known as Iron Dome has proven its capabilities almost nightly as it knocks down volleys of Hamas rockets during the war with Hamas.

The appeal of a similar missile shield for the U.S. is obvious, especially for a presidential candidate with a penchant for massive defensive infrastructure projects, like his signature border wall along the U.S.-Mexico border. And it fits with Trump’s message that the world is a dangerous place full of dangerous enemies who are trying to harm Americans and that only he is willing to do what it takes to protect them.

However, the U.S. military has already poured hundreds of billions of dollars and decades of research into missile defense development with only limited results and certainly nothing approaching the kind of impenetrable “giant dome” over the entire country that Trump promises.

“We’re seeing a lot of positive news on missile defense. It’s doing really good work on protecting civilians in Ukraine and Israel now,” said John Erath, a former National Security Council official who is the senior policy director for the Center for Arms Control and Non-Proliferation, a nonpartisan nonprofit group. “But what is going on there is far different from what is being worked on and planned and may someday come to pass defending the U.S. homeland. It’s apples and oranges.”

Since the 1980s, the U.S. military has experimented with myriad ways to shoot down missiles, from space-based weapons to robot Gatling guns to jumbo jets with laser beam emitters mounted on them. The U.S. has also built enormous radar systems in remote parts of the Arctic to detect and track incoming missiles for possible interception. And some of the world’s most powerful supercomputers and smartest scientists at the Massachusetts Institute of Technology have been running calculations.

After all that, the U.S. and other military powers like Israel have gotten good at shooting down short-range missiles coming from nearby, but they have minimal capacity to stop the kinds of longer-range threats the U.S. faces.

Israel’s Iron Dome’s is designed to intercept projectiles fired from no more than 43 miles away, according to a 2023 Congressional Research Service report. Each battery is designed to defend a maximum area of about 60 square miles, a little less than the size of Washington, D.C.

That’s perfect for Israel, a small country, which is worried about missiles being fired from the nearby Gaza Strip or West Bank.

But for the U.S. homeland, Iron Dome would solve a problem America doesn’t have, because it isn’t generally concerned about Mexico or Canada lobbing missiles at border towns.

The U.S. military has its own short-range missile defense systems like Iron Dome, and it has even purchased several Iron Dome batteries to test them, but they’re used for what it calls “point defense” — defending specific locations like overseas U.S. military bases and naval ships.

The continental U.S. is 450 times bigger than Israel, and it is threatened by intercontinental ballistic missiles fired from places like Russia or China, not short-range ones from neighbors. Those are a completely different kind of threat that the Iron Dome isn’t designed for.

“Those missiles go over the North Pole and then into space before re-entering the atmosphere on the way to their target,” Erath said. “While Hamas rockets might be traveling several hundred miles an hour, intercontinental ballistic missiles re-enter from space at thousands of miles an hour.”

At those speeds and trajectories, reliably hitting them is vastly more challenging.

“We have invested billions in missile defense systems, and we have certain capabilities against very limited missile threats against the U.S. homeland,” Erath said. “If there were an accidental launch or a rogue actor got a handle of one or two, yeah, we can protect against that. But if you’re talking about a mass attack from a country on the scale of Russia or China, the math just doesn’t work out.”

With current technologies, defenders are at a major disadvantage, Erath said, because reliably hitting an incoming missile generally requires launching at least three interceptors, because each one has a relatively low probability of success. But interceptors cost more than the missiles they’re trying to hit, because they require more advanced guidance systems, and you need more of them.

“So you need a lot of them, and they’re expensive, and the antidote to that is very simple, which is: You just throw more things at us and overwhelm the defenses,” Erath said.

Military officials have been transparent about that, especially as the U.S. has been scrambling to send more Patriot and Terminal High Altitude Area Defense, or THAAD, anti-air batteries to Ukraine, each of which are enormously expensive.

“Simply put: We cannot defend everything,” Army Reserve Lt. Gen. A.C. Roper, the vice commander in charge of U.S. aerospace defense for North American Aerospace Defense Command, told a think tank audience last summer, according to Inside Defense. “Placing a Patriot or THAAD battery on every street corner is both infeasible and unaffordable.”