Why isn't Andrew Napolitano defending Trump on immigration?

Fox News senior judicial analyst Andrew Napolitano said Monday that President Trump cannot legally follow through with his threat to shut down the U.S.-Mexico border.

“He cannot legally do it," Napolitano said on Fox News. "We know that because of federal statutes. They were last revised in 1986 when our relationship with migrants coming north was very different than it is now."

“But that’s the law as he finds it and that’s the law as he is required to enforce it," Napolitano continued. "And that’s the law that the federal judge in San Francisco that the president attempted to disparage by calling an ‘Obama judge’ told him he had to enforce as well.”

Napolitano noted that Trump doesn't have to tolerate "lawlessness," but said that according to the law, migrants who have a "bonafide asylum claim, meaning you are escaping a government that is pursing you, or escaping a government that is failing to enforce basic law and order, can enter the U.S."

“The president doesn’t want to hear this but it’s the law,” he added.

  The Hill

I assume there will be lawsuits over the use of tear gas against those people who tried to cross recently.