In 2011, after an earthquake and tsunami caused a meltdown at Japan’s Fukushima-Daiichi power plant, Gregory Jaczko, then the chairman of the U.S. Nuclear Regulatory Commission, had to worry about two things: whether radioactive fallout would harm the U.S. and whether a similar accident could befall an American plant. The answer to the first question turned out to be no. The second question preoccupies him still.

The NRC directed the operators of the 60 or so working U.S. nuclear power plants to evaluate their current flood risk, using the latest weather modeling technology and accounting for the effects of climate change. Companies were told to compare those risks with what their plants, many almost a half-century old, were built to withstand, and, where there was a gap, to explain how they would close it.

That process has revealed a lot of gaps. But Jaczko and others say that the commission’s new leadership, appointed by President Donald Trump, hasn’t done enough to require owners of nuclear power plants to take preventative measures—and that the risks are increasing as climate change worsens.