Highlighting his opposition to nuclear power ahead of the Empire State’s primary later this month, Bernie Sanders is calling for the shutdown of a nuclear power plant outside New York City that has leaked radioactive material into groundwater supplies.

The Indian Point plant has long been a source of controversy, thanks to numerous leaks and safety concerns. In February, New York Gov. Andrew Cuomo called the latest leak at the plant “unacceptable.” But the plant produces about a quarter of the electricity used by New York City and neighboring Westchester County, making it difficult to replace.

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“I am very concerned that the Indian Power nuclear power reactor is more than ever before a catastrophe waiting to happen,” Sanders said in a statement Monday. “In my view, we cannot sit idly by and hope that the unthinkable will never happen. We must take action to shut this plant down in a safe and responsible way. It makes no sense to me to continue to operate a decaying nuclear reactor within 25 miles of New York City where nearly 10 million people live.”

view photo essay The presidential campaign: Bernie Sanders The self-described democratic socialist is known for pushing change on income inequality, college affordability and criminal justice reform.

“Even in a perfect world where energy companies didn’t make mistakes, nuclear power is and always has been a dangerous idea because there is no good way to store nuclear waste,” Sanders said. “That is why the United States must lead the world in transforming our energy system away from nuclear power and fossil fuels.”

Sanders is the only candidate in either party who wants to end nuclear energy production, which currently accounts for 20% of U.S. electrical generation. But this is the first time Sanders has leaned into the issue in a high-profile way as a potential wedge issue between rival Hillary Clinton and the Democratic base.

Sanders wants to replace nuclear with clean renewable energy, like wind and solar. But some environmentalists have called his opposition to nuclear power misguided, arguing nuclear is a good alternative to fossil fuel before renewables can take up the slack.

A narrow majority of Americans favor nuclear energy, while 43% oppose it, according to Gallup. That’s down from a peak in 2010, when 62% supported nuclear power, undermined by the 2011 Fukushima disaster in Japan. Wind and solar energy are highly popular in polls.

Hillary Clinton, whose Chappaqua home is just about 15 miles from the plant, was one of the most vocal critics of Indian Point while she served in the Senate. “Just about every week we pick up the local newspaper and find some other problem at Indian Point,” Clinton said in 2007 as the plant faced a relicensing battle.

But Clinton called for improving operations at the plant rather than shutting it down entirely.

Sanders has used local energy issues, generally pipelines, in past contests to galvanize his supporters and draw contrasts with Clinton.

In Iowa and New Hampshire, he campaigned against pipelines that had general local opposition. In Minnesota, he came out against two Enbridge Pipelines, which he said would a similar impact on climate change as the Keystone XL pipeline.