Despite impending partial implementation, Trump's travel ban faces challenges

— -- The Supreme Court today agreed to review two lower court's rulings on President Donald Trump's travel ban when it reconvenes in the fall, but until then the president's travel ban faces potential implementation challenges.

The court granted the Trump administration's request for a stay in part, allowing a 90-day ban on foreign nationals from six predominantly Muslim countries and a 120-day halt on the U.S. refugee program to go into effect, with the exception of “foreign national[s] who have a credible claim of a bona fide relationship with a person or entity in the United States.”

It's a compromise but the travel ban could be difficult to enforce, according to ABC News' legal consultant and law professor Kate Shaw.

Part of Trump's travel ban will presumably go into effect in 72 hours, or on Thursday. At that point, the 90-day and 120-day time periods will start running. However, the Supreme Court isn't back in session to hear arguments on the travel ban until October.

During that time, it will be up to Department of Homeland Security officials and the district courts to interpret which individuals have a "bona fide" connection to the United States.

According to Shaw, the road ahead might include "a lot of litigation over the summer about who exactly has enough of a connection to satisfy the Supreme Court standard."

The government will also proceed with a worldwide review of its vetting procedures, as laid out in the executive order. The Supreme Court agreed with the Ninth Circuit that that review "may proceed promptly, if it not already underway."

The executive order gives the Department of Homeland Security 20 days to review and 50 days for foreign governments to bring their practices in line.

The Supreme Court said the administration should have enough time to “conclude its internal work and provide adequate notice to foreign governments" by the end of 90 days, when the ban on entry from the six countries expires.

The Trump administration could try to make the travel ban permanent after its vetting review.

"The question is whether President Trump re-issues the ban, or some similar order, to keep the dispute live going forward," said Stephen Vladeck, a law professor at the University of Texas School of Law.

If Trump doesn't attempt to keep the travel ban alive after the 90-day period, the case could be moot before the Supreme Court hears it on the merits in the fall.

"There's a very good chance that, by the time the justices once again consider this issue, there’s nothing left for them to do," Vladeck said.