After more than 50 years as one of the country's landmark environmental laws, the Endangered Species Act has gone from one of the most popular measures before Congress to one fueling demands that it be revised, if not discarded.

The National Parks Traveler is reviewing the Endangered Species Act's work and its record, spotlighting individual species that it's protected, those that it failed, and those that it recovered.

The monthslong series comes as ESA champions worry that the push to weaken the law could consign countless animals and plants to the growing list of flora and fauna that, like the Passenger pigeon, are now found only in books and online.

The National Park System seems to be the perfect background to explore these questions, as its lands are supposedly the best preserved on the federal landscape.

I recently interviewed two wildlife advocates — Jake Li, a vice president with Defenders of Wildlife who spent time working in the Environmental Protection Agency and U.S. Fish and Wildlife Service before joining the advocacy group, and Stephanie Adams, director of wildlife at the National Parks Conservation Association.

Though the interviews were done separately, the questions were largely the same. What follows is a merging of those two conversations.