Given the furor sparked by President Trump's disgraceful "Obama judges" tweet, and Justice Roberts' extraordinary (and most welcome) stern rebuke [see here], it is easy to lose sight of the legal issues involved in the case, and in the opinion by Judge Tigar [available here] that so enraged the President.
It's actually not all that complicated. On November 9, the President issued a Presidential Proclamation [available here], and DHS announced a series of new rules, that had the combined effect of making "any alien who enters the United States across the southern border" categorically ineligible to bring a claim for asylum, unless they entered the country at a "port of entry" - i.e., a US Border and Customs Patrol-operated facility - on the US-Mexico border.
The Immigration and Naturalization Act provides:
Any alien who is physically present in the United States or who arrives in the United States (whether or not at a designated port of arrival and including an alien who is brought to the United States after having been interdicted in international or United States waters), irrespective of such alien's status, may apply for asylum in accordance with [the procedures set forth elsewhere]." 28 U.S.C. § 1158(a) (emphasis added)
That's pretty much it. You be the judge. I'm no expert in Immigration law, and I suspect you're not either. But it doesn't look that complex. Congress has clearly said, in the statute, that "any alien" arriving at the border is eligible to apply for asylum, whether or not he/she enters at a "point of entry." The Executive Branch has declared that for certain aliens - those entering across the US-Mexico border - that will no longer be the case.
This what Trump is so outraged about? This is Separation of Powers 101. Congress (with, of course, Presidential approval) makes immigration law; the President is charged with "faithfully executing" that law. Here, he has overriden an express Congressional directive regarding the eligibility of aliens for asylum. He can't do that, on his own.
It's beyond ironic that Trump has chosen this case for a rant about how badly he is treated by all those "Obama judges" there on (or in) the 9th Circuit. He loses this case before a "Bush judge" or a "Trump judge" or a "Reagan judge" - i.e., before any judge who takes the Constitution at all seriously. Trump doesn't much like the Separation of Powers, I get that - and he's surely going to be liking it a lot less now that the Democrats control the House. But he better learn to live with it, for all of our sakes.