Throughout history, a few monuments have become the source of political conflict. In 1915, for example, Woodrow Wilson cut down the boundaries of Roosevelt’s designation of Mount Olympus National Monument, much to environmentalists’ dismay. This past April, Trump called former President Barack Obama’s designation of Bears Ears National Monument, an area of more than 1.3 million acres in Utah, an “egregious abuse of power.”

In his assessment, Zinke proposed shrinking Bears Ears from 1.35 million acres to roughly 160,000, saying changes would “provide a much-needed change for the local communities who border and rely on these lands.” Still, environmental groups have pledged to fight Trump in court if he follows through on the recommendations.

I spoke with Mark Squillace, a law professor at the University of Colorado Boulder and former assistant to Bruce Babbitt, the interior secretary under President Bill Clinton, about the unprecedented territory the Trump administration has entered into—and the history behind a significant presidential power. Our conversation has been lightly edited for length and clarity.

Lena Felton: Let’s start at the very beginning and go back to the Antiquities Act of 1906. What was the significance of Congress granting the president sole power to protect sites?

Mark Squillace: I think it’s fair to say that people weren’t exactly sure about the breadth of the Antiquities Act when it was passed, but there clearly was a desire on the part of some of the people that were pushing this legislation to have more expansive authority than the narrow protection of small sites around our archeological digs. There clearly was some interest in kind of a broader type of legislation.

A large part of the reason for the Antiquities Act was to allow the president to act quickly to protect land. We can get into this later, but the big debate right now is whether it’s a one-way protection or whether the president somehow has the authority to undo protections made by previous presidents. If you think about the fundamental reason for the law in allowing quick protection before somebody can come in and undermine those protections by building roads, by locating mining claims, by logging timber, whatever they might want to do—you need to act quickly, and you need to do it in a way that’s protective.

Felton: Can you talk a bit about Theodore Roosevelt’s role in being the first president to use that power?

Squillace: The designation and decision that Roosevelt makes in 1908 to proclaim the Grand Canyon National Monument was one of the things that really changed the history of the Antiquities Act going forward. The Grand Canyon National Monument in 1908 was over 800,000 acres when it was designated, and it fairly soon thereafter led to a lawsuit by a guy by the name of Ralph Henry Cameron, who had located some mining claims around the Grand Canyon.