Updated

Native American tribes and environmental groups preparing for a legal battle to stop President Donald Trump from dismantling Utah's new national monument will face a tougher challenge than anticipated.

Utah Republican officials who oppose Bears Ears National Monument asked Trump to rescind it, something no president has tried before.

But U.S. Interior Secretary Ryan Zinke has instead recommended Trump shrink Bears Ears, something past presidents have done 18 times to other monuments.

Legal experts disagree on whether the law allows a president to downsize a monument, and it's something that has never been challenged in court.

Environmental groups and others gearing up for a court fight say they think the law is on their side, but others, including Utah Republicans, disagree.