The Hill online journal is reporting, based on observations made during oral argument, that a majority of the Supreme Court may find that "Trump Travel Ban 3.0" is lawful and constitutional. If so, this is excellent news, although of course only time will tell us for certain.
The Hill quotes Justice Sonia Sotomayor as asking of the government's counsel during the oral argument, "Where does the president get the authority to do more than Congress has already decided is adequate?"
That is such an excellent question! I wonder why the good justice wasn't so concerned about the answer to that question when she voted with three other justices to sustain President Obama's Deferred Action for Parents of Americans and Lawful Permanent Residents (DAPA) — the Deferred Action for Childhood Arrivals (DACA) look-alike program, only for parents and adult relatives instead of minors.
Like DACA, that program had no statutory basis, instead relying on a vague notion of "prosecutorial discretion", although it stood that concept on its head by making discretion the rule rather than the exception for hundreds of thousands of illegal aliens. And yet Justice Sotomayor was among those who voted in favor of seeing it implemented. Unfortunately for them, the vote ended up in a 4-4 split decision because the ninth seat on the Court had been vacated by Justice Scalia's death and not yet filled by Neil Gorsuch.
The result of the split was to uphold the decision of the lower Fifth Circuit Court of Appeals, which had sustained the request by a consortium of states led by Texas to enjoin its implementation.
But this was no thanks to Justice Sotomayor or her other liberal-leaning justices (including Justice Elena Kagan, who chose not to recuse herself despite her ties to the Obama administration, where she was for a period Solicitor General prior to elevation to the court), all of whom were untroubled by the lack of a statutory basis or congressional resolution or any other indicator that the president hadn't exceeded "the authority to do more than Congress ha[d] already decided is adequate".
Now back to Justice Sotomayor's question in reference to the so-called "Travel Ban, version 3": The answer can in fact be found in statute – which surely Justice Sotomayor knows, unless she was the victim of poor research by her law clerks in preparing for this case, or she just didn't care enough to read the briefing materials. By enacting Section 212(f) of the Immigration and Nationality Act, 8 U.S.C. Section 1182(f), which states in pertinent part, Congress made its will known:
(f) Whenever the President finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States, he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate.
So apparently Congress did cede to the president the powers needed to initiate executive action of the sort being considered by the Court, and in a way consistent with both the law and Constitution, contrary to both DAPA and DACA.