Accepting the GOP presidential nomination in Milwaukee on Thursday night, former President Donald Trump pledged to “build an Iron Dome over our country and we’re going to be sure that nothing can come and harm our people. And again, from an economic development standpoint, we’re going to make it all right here.” Trump twice emphasized that the missile defense system would be made entirely in the United States.

This rhetoric surely sounds good to Americans who are fearful of escalating tensions with Russia and who have witnessed the striking success of Israel’s Iron Dome air defense network against Hamas and Hezbollah. The problem is that building an encompassing missile defense system for the entirety of the U.S. is impractical. At the intersection of capability and costs, it just wouldn’t work. It would also catalyze an already exacerbating nuclear arms race between the U.S., China, and Russia.