President Donald Trump has made rebuilding the U.S.’s nuclear industrial base a central part of his energy agenda. Last week, a nuclear startup operating in Emery County, Utah, took an important step toward making that revival real. Valar Atomics became the first Department of Energy-authorized reactor built outside a national laboratory to reach “criticality.”Valar successfully completed a zero-power-fueled criticality demonstration, which means its reactor sustained a controlled nuclear chain reaction at very low power. The milestone does not mean the reactor is yet producing commercial electricity, but it is still a major step. It is the nuclear equivalent of starting an engine for the first time: The car is not yet on the highway, but the machine has come alive. Valar says it aims to produce power by July 4.The United States used to be the world’s leader in nuclear power. America pioneered the nuclear age. But that leadership has eroded. The White House notes that it took nearly 40 years for the U.S. to add as much nuclear capacity as another developed nation managed in just 10. As American nuclear power has slowed, other countries have stepped into the void. According to the White House, 87% of nuclear reactors installed worldwide since 2017 are based on designs from two foreign countries. Not only has the U.S. fallen behind on nuclear design, but it has also become dependent on foreign sources of uranium and uranium enrichment.