Yesterday, President Trump signed an executive order requiring a review of the large national monuments that have been created over the last 21 years. The president ran on a platform of reducing regulations to promote jobs and economic growth, but he inherited vast areas -- nearly a billion acres in total -- that have been shut off from productive use under the Antiquities Act.

His predecessor, Barack Obama, was the king of Antiquities Act abuse, designating more monuments covering more area than any prior president. He tripled the total area restricted, adding more than 500 million acres in new and expanded monuments. Most of this area was locked up during the last year of Obama's presidency, once he was no longer accountable to voters.

There's a reason presidents designate "midnight" monuments at the end of their terms: they can be extremely controversial when people depend on the use of areas being closed off to support their families.

Take Bears Ears National Monument. In the final weeks of his presidency, President Obama declared 1.35 million acres in Utah off-limits, over the objections of the governor, Utah's congressional delegation, and local governments. Shortly before, a poll found that only 19% of Utahans supported the monument. The unilateral decision also derailed a legislative compromise that had been in the works for years.

The controversy has led to calls for President Trump to reverse the damage done by his predecessor under the Antiquities Act. According to a recent American Enterprise Institute paper authored by Todd Gaziano and law professor John Yoo, President Trump may revoke or substantially shrink controversial monuments under the Antiquities Act.

The suggestion that some of these controversial monuments may be reconsidered has caused alarm among environmental groups, who routinely lobby for more and more monuments. They blithely assumed that these decisions were permanent and insist that they must be because no president has previously revoked a monument.

On one level, the argument that the president has this authority is obvious. Suppose, for instance, that a monument was created to protect an artifact that has since been excavated and taken to a museum, removing the monument's justification. Or imagine a president designates a monument to protect what he later learns was a hoax. What sense would it make to forever forbid the use of federal lands in such circumstances? And what if a president declares a monument that violates the Antiquities Act?  Are subsequent Presidents forever bound by that illegal action? Of course not.

There are many reasons to question some of President Obama’s monument designations. The Antiquities Act, as its name suggests, was adopted in 1906 to allow the president to act quickly to protect Indian and other historic artifacts threatened by looting. But today, presidents declare monuments based on fish, trees, and vistas.  The statute also limits monuments to “lands owned or controlled by the Federal government” but several huge monuments have been designated on the oceans.  Finally, the statute requires monuments to be confined to “the smallest area” compatible with protecting it, yet they routinely exceed a million acres.

The president can undo or shrink a monument if he believes it's in the nation's best interests.

Environmental groups opposing the president’s power to revoke monuments principally argue that this power would be inconsistent with the Antiquities Act’s preservation purpose. Of course, a statute’s purpose is in the eye of the beholder and any such argument should be met with skepticism. People conveniently tend to see a statute’s purpose as adopting their political preferences.

Opponents of the president's authority to undo a monument ignore that the Antiquities Act never requires the creation of a monument in any circumstances. It restricts the president's power to designate monuments, to be sure. But, within these limits, the statute leaves the decision to create a monument to the president's discretion. He may consider the impact of a monument on jobs, economic growth, and anything else he wishes.

If the Antiquities Act allows presidents to decide against creating a monument based on these factors, how can it be contrary to the statute's purpose to use the same factors in deciding to undo or shrink a monument? It cannot be. When presidents have this sort of open-ended discretion to act, they have the same discretion to reconsider even where, as here, they are acting pursuant to power delegated by Congress.

For instance, when a statute delegates to the president or an agency he oversees the power to adopt discretionary regulations, the same discretion applies to the repeal or reform of those regulations. Discretionary regulations are only immune to future president's reconsideration in the rare circumstances where Congress expressly states that it should be so.

Congress has given no indication that that president's open-ended discretion to create a monument (or not) does not also authorize the president to exercise the same discretion for undoing or shrinking monuments.

Consistent with this background rule, several presidents have shrunk existing monuments, sometimes dramatically, even though the statute does not expressly authorize them to do so. In the first few years after the statute was enacted, President William Taft created the Navajo National Monument only to later shrink it by almost 90 percent. A quarter of the presidents elected since the Antiquities Act was enacted have used their power to reduce the size of monuments without anyone challenging those actions.

President Trump has an opportunity to reconsider whether any of the more than 500 million acres President Obama locked up could be better put to creating jobs and economic growth. If he does, he could provide relief to rural voters. And he can create the political momentum for Congress to finally reform the Antiquities Act so that those areas that truly need permanent protection can receive it while preventing future presidents from abusing their power against the needs of people's.

Jonathan Wood is an attorney at Pacific Legal Foundation and represents several fishing organizations in a challenge to the Northeast Canyons and Seamounts Marine National Monument.