WASHINGTON -- Edward Snowden broadened his search for sanctuary this week, but finding an escape from his current state of limbo in the Moscow airport would take a combination of political will and legal savvy that immigration experts said may be hard to come by.

Snowden, 30, the former National Security Agency computer specialist who released classified files exposing the worldwide scope of U.S. surveillance systems, remains in the transit zone of the airport mulling what appear to be dwindling options.

Tuesday evening, a plane carrying Bolivian President Evo Morales was prevented from refueling in Portugal and instead re-routed to Austria en route home because of fears Snowden was on board, Bolivian officials told several news organizations.

Experts on refugee and asylum issues said Snowden’s ordeal is turning into a law school case study that challenges the definition of a refugee, tests the strength of extradition treaties, looks at when it’s OK to revoke passports, and examines the ethics of U.S. interference in a process that’s designed to allow persecuted people a chance to plead their case.

Snowden reportedly has applied for asylum in 21 countries, but so far there are no takers. Poland, Brazil, India and Finland each rejected the petitions outright. Russia agreed to consider Snowden for asylum if only he’d stop publishing items from his trove of classified U.S. files; Snowden balked and withdrew his petition.

Austria, Ecuador, Norway and Spain have said they’d consider Snowden’s application if the requests were made within their territories – a convenient if rather disingenuous way to wash their hands of the matter, analysts said. And another dozen – including China, France and Germany – have yet to issue responses.

Morales so far has offered the most solid promise yet by agreeing to “shield the denounced,” as he was quoted by news agencies while on a trip to Russia. Venezuelan President Nicolas Maduro, also in Russia, similarly praised Snowden and said he deserves a “humanitarian medal” for exposing the NSA’s extensive spy network.

But that tacit support doesn’t move Snowden any closer to the transit lounge’s exit. Bolivia or Venezuela would have to figure out how to get him to their embassies – a move his Russian hosts have been reluctant to facilitate – to issue him a temporary travel document called a letter of safe passage, which is typically honored by carriers and countries in cases of refugee resettlement.

Even winning approval to settle somewhere would be just a first step, immigration specialists said. It’s debatable whether he could build a case for refugee protections, they say.

“What it boils down to is: there’s the law, and then there’s the politics behind the law,” said David Leopold, general counsel for the American Immigration Lawyers Association. “If any one of these countries decides to give him safe haven, they can do so and there’s not much the U.S. can do about it except complain diplomatically.”

The Obama administration is pre-emptively working just that track, leaning heavily on nations to prevent Snowden from using their territories to escape the felony charges that await him back home. U.S. officials are determined to close off all potential routes and force his return before he can argue his case.