A lot of people probably don’t realize that 2 of the 4 reactors at Three Mile Island have been operational without issues since the 1970s. They are projected to be shut down next year.

Across the U.S., more communities are grappling with such questions, as the owners of nuclear plants dating back to the 1960s and ’70s begin to put their facilities into premature retirement. That’s because the plants are having trouble staying competitive in an era of cheap natural gas, a product of the shale boom. Also, nuclear power’s attraction as a clean energy source has been eclipsed by no-emissions alternatives such as wind and solar power.

One enemy of the nuclear industry in Pennsylvania is natural gas lobbyists.

Even so, nuclear advocates have thus far had better success mobilizing resources at the state level. In Illinois, the state that leads the U.S. in nuclear power generation, lawmakers passed controversial legislation in 2016 to subsidize nuclear plants with so-called zero-emission credits. Exelon, which operates the largest nuclear fleet in the nation, owns the state’s six operational sites.

States including New York and New Jersey have enacted similar policies. Pennsylvania has been a tougher sell. A nuclear energy caucus in the state legislature has failed to pass anything helpful yet. Its efforts have been stymied, in part, by forces supporting the state’s booming natural gas industry.