There are several old sayings in English to apply to this decision: third time is the charm, and the devil dwells in the details. But first, what was the decision?
Briefly, the Supreme Court, in a 5-4 vote, affirmed the legal right of the the President to exercise authority over entry into the U.S. by foreign nationals as delegated to him by Congress under the law. The Supreme Court did not say it agreed with the policy. (Justice Kennedy, one of the justices who voted in the majority, made it clear in his concurring opinion that he finds the policy questionable at best – and he was being polite.) It is essential to understand that the role of the Supreme Court is not to make law or to establish policies, but to render a decision on whether laws passed by the U.S. Congress (legislature) do not violate the Constitution and that implementation of law by the Presidency (executive) follow the laws as passed by Congress.
In this decision, the Justices found that this third iteration of the travel restrictions, which temporarily banned persons from certain nations from entering the U.S., fell within the legal authorities Congress had given to the President. In large part, this was due to the revisions that had been made following the first two travel restrictions the President Trump had ordered. One possibly helpful analogy is that the first and second versions had so many “bugs” in the programming, that they crashed. Learning from their mistakes, and bringing in some talented coders, the White House eliminated the bugs just enough to produce a workable though balky App, just good enough not to crash. One re-write is a mechanism for those banned to seek a waiver of the provisions of the ban. Reportedly several hundred persons have appealed the ban and been able to travel to the U.S. since its proclamation in September 2017. Another important detail is which countries’ nationals are subject to the restrictions. They are Iran, Libya, Somalia, Syria and Yemen, North Korea and certain officials of Venezuela. Chad, Iraq, and Sudan were on the list but have been removed based on improvements in cooperation with U.S. border security agencies.
So, third time, after two failures and with considerable re-writing, is the charm. But the success (charm) for Trump is very circumscribed, certainly nothing like the intent in the first effort at a travel ban.
And, the devil dwells in a few very important details – the Court, not the President, decides on the interpretation of the law and has reasserted its authority to block presidential action if such action does not follow the law as passed by Congress. Most important, the Court made clear that a travel ban based on religion would be unacceptable, and only because this iteration of the travel restrictions includes a case-by-case waiver process and is specifically targeted at countries unable or unwilling to do security background checks on their citizens wishing to travel to the United States, does is cross the threshold (barely) for presidential legal authority. (In the case of Venezuela, the list targets suspected drug traffickers in the government and others who have thoroughly destroyed the democratic structures of that nation.)
What’s next? Will Trump expand this to other countries? Not likely, as to do so, he would have to show that the expansion to other persons or countries met the national security protection standards of the current 3rd iteration that the court allowed. Politically, very unlikely. Trump likes to win, and he’ll count this as a win, tell his supporters the Court agreed with him and not with the so-called open-border advocates that he likes to malign , and move onto other more urgent projects (Iran sanctions, North Korean nukes, etc.).