President Donald Trump has authority under the Constitution, which the Supreme Court has recently affirmed, to deal with the approaching migrant caravan by issuing an executive order barring entry into the United States by any man, woman or child for any reason — or no reason.

End of the caravan problem? No. Thanks to the sad state of America’s immigration laws and regulations, Trump’s executive order would be stopped immediately by an avalanche of litigation, led by the American Civil Liberties Union (ACLU).

Unstoppable force, meet immovable obstacle.

Approximately 10,000 people are with the caravan, according to the latest estimates. Trump is mobilizing the military along the border and ending U.S. aid to countries that don’t block the caravan.

“We feel he has the right to deny them entry, he has the right to keep them on the Mexican side of the border, he has the right to set up makeshift civil detention areas to hold them during a three-day period while they adjudicate claims,” Federation for American Immigration Reform (FAIR) President Daniel Stein told LifeZette.

Trump reportedly is considering an executive order along those lines, but it’s not known how seriously the approach is being taken.

“But this is the problem. The minute they get on U.S. soil, the ACLU goes to work challenging the legality of the detentions, the conditions of the detentions, the conditions of detained minors, and then there is the Flores court case.”

Trump has been challenged on his power to restrict immigration throughout his presidency, and the caravan is no different. Federal immigration laws allow the president to suspend the entry of all aliens or any class of aliens. But critics argue he must heed international agreements to process credible asylum claims.

Related: Hill Immigration Republicans Wary of Approaching Migrant Caravan

“Some people say, under U.S. statuary law, everyone who makes a credible fear case has to be given a court date for an asylum hearing, which, of course, means they’re gone for years, and that’s exactly why the caravan exists,” Stein said.

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“We have these ludicrous asylum standards, a lack of detention space, we have no interior enforcement, and we have sanctuary cities. All of these things have been set up to incentivize people to use these loopholes to get into the country.”

Center for Strategic and International Studies senior fellow Richard Miles said illegal border crossers are still entitled to make asylum claims that must be processed. The claimant has to be interviewed, but, once they are in the U.S. immigration system, things get much more complicated.

“There’s no easy solution here,” Miles told LifeZette. “The best-case scenario would be Mexico would allow processing of these asylum requests on their side of the border so that we don’t have a situation where they apply for asylum, they’re denied and then the U.S. has to figure out where to house them until they’re deported.”

Miles pointed out “that’s when you get a real headache for the United States. Now the Mexicans don’t want that headache, either, so they’re not wild about the idea.”

How and where the caravan approaches the U.S. border could determine the response. Those in the throng are likely to head for a port of entry such as Brownsville, Texas, but they could also scatter to cross illegally at different points.

“If they make it to Mexico City and are still sizable, then at that point they’re going to decide which entry point to head for,” Miles said. “The closest one will be Brownsville but they can choose others and they can still try to get smuggled across the desert.”

Miles believes the caravan’s size is likely to decrease as it approaches the border, and that the migrants are likely to approach a point of entry since that gives them more legal protections. Crossing illegally has become more risky and expensive in recent years, thanks to human traffickers and drug cartels.

“Our border patrol is much better equipped and a lot more numerous than the Mexicans did on their southern border with Guatemala,” Miles said. “So those shots of migrants just pushing past police, we’re not going to see that in Brownsville. Essentially, what the migrants will have to do is wait and hope they can get processed for asylum.”

Stein argues Trump can take whatever measures are necessary to deport every immigrant who doesn’t make a prior asylum claim in another country, primarily Mexico. Without the prior claim, the president is not beholden to the international agreements critics cite.

“The president has the right to line up a bunch of planes in airfields and military bases and escort them onto planes and fly them back home unless there is evidence they made an asylum claim in another country on the way up.”

“The president has the right to line up a bunch of planes in airfields and military bases and escort them onto planes and fly them back home unless there is evidence they made an asylum claim in another country on the way up,” Stein said.

“International law, in our view, does not require the United States to entertain an asylum claim for anyone who failed to make a claim in another country where they might have made one,” Stein said.

Former federal prosecutor Sidney Powell believes Trump should immediately issue an executive order that stops all immigration until the present system can be fixed.

“I think the president needs to issue an executive order within the next couple of days that makes it clear that we’re not accepting any more immigrants, period,” Powell told LifeZette. “He doesn’t even need to specify a time, he can just say, ‘We’re closed, the door is closed, we’re not taking any more applications of any kind, asylum, refugee or otherwise.'”

But even that order by Trump would likely be tied up in litigation.

“We’ve had court challenges against everything from invoking Temporary Protected Status (TPS), defunding sanctuary cities, and it goes on and on,” Stein said. “And we have these politicized judges who are just taking their political perspective and using that to issue these injunctions to slow Trump down.”

Related: Trump’s Options Will Plummet if Migrant Caravan Crosses Border

Stein notes that, with all these legal restrictions, the country has essentially willed itself into the current situation, and the president is right to be mad. Powell argues now is the right time to bar all immigration since the Supreme Court made clear the president has that power when he was sued for blocking entry to individuals’ travel to the U.S. from six predominantly Muslim countries.

“Of course, it would make it more difficult if a court said otherwise, but I think the language of the Supreme Court decision at this point is sufficiently clear, particularly if it’s applied to all immigrants,” Powell said.

“Then there is no room for discretionary analysis. At worst, it is limited to the district of whatever district judge made that order, and at best, I’m not sure the president couldn’t just ignore it and continue litigating it but proceed.”

Trump attempted an earlier crackdown on illegal immigration that resulted in children being separated from the adults who illegally brought them into the country. But that process can often take longer than the 20 days immigration officials are allowed to hold children.

“No doubt about it, this could be another headache for the administration, if, in fact, they get several hundred or even a thousand migrants eventually reaching the border,” Miles said. “But unless Congress decides to change the law or the administration refuses to process interviews, we’re probably going to see a replay of what we saw in the spring.”

In other words, Trump is almost certainly stuck between a rock and a hard place.

“Unless Congress changes the law, the administration is going to have to follow the procedure, and my guess is they’re not going to want to have another political disaster on their hands of separating families,” Miles said.