One of the nations largest utilities last month announced plans to request new licenses for 11 nuclear reactors, setting up a critical new test for Democratic presidential candidates on how to achieve zero-carbon energy generation.

Duke Energy, headquartered in Charlotte, North Carolina, said it plans to submit its renewal applications for reactors at six power plants in the Carolinas starting in 2021, which could put those decisions in the hands of a new White House if a Democrat unseats President Donald Trump next year.

As it stands, its unclear where the top contenders for the Democratic presidential nomination would stand on relicensing. Despite intense focus on energy and climate policy, on which there are clear divisions among the candidates, the issue of nuclear power has largely been ignored in the Democratic debates. Sen. Cory Booker (D-N.J.) and businessman Andrew Yang are all in, pledging to keep open safe plants and invest heavily in researching advanced reactors. On the opposite end of the spectrum is Sen. Bernie Sanders (I-Vt.), who promised to halt construction on new reactors and issue a moratorium on nuclear plant license renewals.

The views of the candidates in between are less certain. Sen. Elizabeth Warren (D-Mass.) endorsed erstwhile climate candidate Jay Inslees proposal, which calls for keeping existing nuclear plants open. But at a CNN town hall last month, she vowed to start weaning ourselves off nuclear energy with the goal of shutting down existing plants by 2035.

Former Vice President Joe Biden, long a critic of the nuclear industry, proposed new funding for advanced reactors but hasnt taken a definitive position on extending the lives of existing nuclear plants.

Warren and Biden, now the top two in several polls, gave unclear responses to The Washington Posts survey on nuclear energy. The Biden, Warren and Sanders campaigns did not respond to requests for comments on the record.