You’ve probably heard that Bernie Sanders has the most impressive climate agenda of any major-party presidential candidate in history. His proposals may be politically unrealistic, but they are bold. If Sanders were president and he had a pliant Congress, his carbon tax and investments in renewables would radically overhaul our energy system for the better.

But some enviro wonks say there is a serious defect in Sanders’ plan: his approach to nuclear energy. He has called for phasing out all U.S. nuclear power plants, which currently account for 19 percent of our electricity portfolio. Nuclear energy has plenty of problems: reactors can melt down, they are ripe targets for terrorists, they are wildly uneconomical, mining the uranium that feeds them is dangerous and environmentally destructive, and no one wants the spent fuel stored nearby. These are the reasons Sanders has long been an opponent of nuclear energy. A few decades ago, that was a widespread view on the left. But now climate change has become the main concern of many environmentalists, and nuclear energy’s saving grace is that it has virtually no carbon emissions.

Sanders’ own climate plan is, rightly, centered around the goal of transitioning away from fossil fuels. Even given a friendly political climate, that will be an enormous challenge. The U.S. currently gets about 67 percent of its electricity from fossil fuels, so all of that dirty energy must be replaced. Does it make sense to try to transition away from nuclear at the same time — to replace yet another 19 percent of our electric capacity — when nuclear power is not a climate threat?