The Court's jurisdiction only extends to matters of law in which it has authority. This isn't controversial. In John Robert's majority opinion on the Individual Mandate in the PPACA, he cited the oft repeated nostrum from Holmes that "Courts should assume that laws are Constitutional."
Now, that is a weird statement to begin with, and one that Holmes used to uphold laws that liberals agreed with while striking down, without any deference, the ones he didn't like.
But the point, correctly phrased, is still valid: In political matters, the courts are to defer to the political branches. That means that the Trump Administration is under NO OBLIGATION WHATSOEVER to prove that his travel ban will accomplish its purpose. The 9th circuit -- and every other Federal Court -- is required to accept that this decision will accomplish its stated goal, even if they don't think so themselves.
Can you even imagine how dangerous it is for the elected branches of government to have to present proof to the judiciary that a law or policy is actually going to achieve its objective? That would place every decision made by someone legitimately representing the People of the United States under the supervision of an unelected lawyer in black robes.