Federal judges on opposite coasts are due Friday to hear legal arguments defending President Donald Trump’s travel ban on citizens from seven predominantly Muslim countries. The ban is sure to reverberate through the courts on a likely path to an appeals court or the U.S. Supreme Court. Here’s a look at how the legal issues may play out:

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Jayashri Srikantiah, a professor at Stanford Law School and director of the Immigrants’ Rights Clinic, said that while the court order appears to clear the way for entry, a more fundamental barrier exists.

“The first step is for them is whether they can obtain a valid boarding pass,” Srikantiah said. “They need to be permitted to board so there can be a discussion at the border about what happens next.”