Without the Endangered Species Act, the restoration of Paiute cutthroat trout to its natural habitat in the high Sierra Nevada would not have been possible.

Had Donald Trump been president in 1973 when the Endangered Species Act became law, California’s Paiute cutthroat trout — the rarest trout in North America — would not exist.

Thanks to the Endangered Species Act, for the past half a century, environmental “harm” has been defined by law not just as human-caused death and damage to individual plants and animals, but also “significant modification or degradation” of their critical habitat. That definition has helped save 99% of organisms listed in the act from extinction. The federal government wasn’t motivated to protect and restore these habitats by goodwill; the act required it to develop recovery plans.

There is arguably no species for whom this provision of the law is more essential than the Paiute cutthroat trout. Its entire native habitat consists of 11 miles of Silver King Creek in the Carson-Iceberg Wilderness high in the Sierra Nevada.

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The Paiute faced imminent extinction in 1975, as they were being slowly hybridized off the planet by non-native rainbow trout. Rainbows had been mistakenly stocked in the Paiute’s habitat in 1949 when a state mule-horse pack train transporting fingerlings took a wrong turn, accidentally releasing them above the natural barrier of Llewellyn Falls.

Because of the Endangered Species Act’s habitat mandate, the U.S. Forest Service, the U.S. Fish and Wildlife Service and the California Department of Fish and........

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