For months, the Biden administration tried in vain to push Russia to release two Americans whom the U.S. considers to be wrongfully detained.

When the Kremlin refused to budge, President Biden made the decision to secure one prisoner's freedom and leave the other behind.

Escorted by intelligence officials from both countries, WNBA star Brittney Griner walked across an Abu Dhabi airport tarmac on Thursday from a Russian plane that delivered her to the United Arab Emirates to an American one that would carry her to freedom. Meanwhile, retired Marine Paul Whelan remained inside a Russian penal colony, where he is serving a 16-year sentence for espionage charges that he and the State Department say are baseless.

Biden emphasized Thursday that he has not forgotten Whelan but he did not have “a choice of which American to bring home.”

“Sadly, for totally illegitimate reasons, Russia has treated Paul’s case differently than Brittney’s,” Biden said. “And while we have not yet succeeded in securing Paul’s release, we are not giving up. We will never give up.”

The inability to bring home Whelan dampened any celebration on Thursday, as did the price of securing Griner’s freedom. In return, the U.S. released Viktor Bout, a notoriously prolific Russian arms trafficker who was serving a 25-year sentence in Illinois for conspiring to kill Americans and providing weapons to terrorists.

The Biden Administration is believed to have initially offered Bout for both Griner and Whelan, but Russia frustrated U.S. officials with its apparent unwillingness to either accept that deal or make a serious counteroffer. White House press secretary Karine Jean-Pierre said the Biden administration had made “every possible offer available” to secure Whelan’s release but “the Russians were not willing to negotiate in good faith.”

“This was not a choice for us of which American to bring home,” Jean-Pierre said. “That was not the choice. It was a choice between bringing home one American or bringing home none.”

This is the second time this year that the Whelan family has been told about a potential prisoner swap only to have it collapse. In April, the U.S. made a deal to free Trevor Reed in exchange for convicted drug-smuggling Russian pilot Konstantin Yaroshenko but were unable to come to an agreement with Russia to make that a two-for-two deal.

The lingering question in the wake of the U.S.’s two failed attempts to secure Whelan’s freedom is why Russia appears unwilling to include him in a prisoner exchange. Is it merely because Russia values Whelan differently because of the espionage charge he is facing? Or is it more than that?

Former State Department foreign services officer David Salvo told Yahoo Sports that Russia had two main objectives during prisoner exchange negotiations: to bring Bout home and to “inflict maximum pain on the Biden administration.” To Salvo, Russia had “all the leverage” with winter approaching at the forced-labor camp where Griner was being held and Biden facing domestic pressure to secure her freedom.

“I don’t think they really believe that Paul is an intelligence officer,” said Salvo, the deputy director of the Alliance for Securing Democracy and an expert on Russian foreign policy. “Honestly, I think the real reason is that keeping him in jail gives them another pawn for future negotiations. They left Paul out of the deal because they knew they could. It’s something else for them to extract leverage over down the road.”

Another potential advantage for Russia of releasing Griner but not Whelan is the opportunity to create backlash for Biden and to sew division and discord in the United States. Danielle Gilbert, a Dartmouth fellow and a leading expert on hostage taking and recovery, said she thinks Russia is “very aware of the issues it’s creating for the White House releasing Brittney Griner, who is a Black, openly gay woman, and not Paul Whelan, who is a white male who has been in prison longer.”

Whatever Russia’s reasoning, the Biden administration owes a debt of gratitude to the Whelan family for the grace with which it received the news that only Griner would be coming home. David Whelan, Paul’s brother, issued a statement on behalf of the family on Thursday backing Biden while acknowledging this was a “catastrophe” for Paul.

“The Biden Administration made the right decision to bring Ms. Griner home, and to make the deal that was possible, rather than waiting for one that wasn’t going to happen,” David Whelan wrote.

Paul Whelan, a Michigan corporate security executive, was arrested in Moscow in 2018 after allegedly receiving a USB drive with classified material from a Russian citizen. While the Biden administration insists that negotiations for Whelan’s release will continue, foreign policy experts say that this was a significant blow to his hopes of securing an early release.

“I don’t know if I could be as magnanimous as the Whelan family,” said William Pomeranz, the director of the Wilson Center's Kennan Institute. “I think this was Paul Whelan’s best chance to get home.”