An Obama administration official just revealed one of the unsavory trade-offs at the heart of the Iran deal

When Rick Stengel, the undersecretary of state for diplomacy and public affairs, went on MSNBC's "Morning Joe" on Monday to talk about "The International Day to End Impunity for Crimes Against Journalists," he probably didn't expect the conversation to turn into a hard-hitting discussion of the Obama administration's Iran policies.

Stengel, the former Time managing editor and a co-author of Nelson Mandela's autobiography "Long Walk to Freedom," went on MSNBC to tout the US's role in creating the day.

But host Joe Scarborough abruptly changed the subject to imprisoned Washington Post reporter Jason Rezaian, whom the Iranian regime has held since July 2014 on trumped-up spying charges. Iranian state TV announced that Rezaian had been convicted last month.

Stengel struggled to explain why the US had been unable to free Rezaian as the result of its diplomatic push with Iran, which culminated in the signing of the Joint Comprehensive Plan of Action on July 14, 2015, about a year after Rezaian was first imprisoned.

He spent some of the interview explaining why Rezaian's plight was less important than the overall nuclear issue. He ended up implying that crimes against even American journalists are at best a mid-level priority for US foreign policy - an especially awkward tactic, considering the point of his appearance was to discuss US efforts to end impunity for crimes against journalists.

"Look at the values and the priorities," Stengel said, as Scarborough and his co-host Mike Brzezinski repeatedly asked why the nuclear negotiations hadn't secured Rezaian's release. "Basically, the secretary and the president were negotiating around a nuclear agreement that could protect the Middle East and the world for generations."

Scarborough responded that the administration's "first priority" should have been the release of US citizens held by the regime.

"I would say the majority of Americans would say, 'OK, listen, how can we trust you on the most important security question of the Middle East during this time if we can't even trust you to do the right thing in bringing Jason home?'" Scarborough said.

"You know what?" Stengel replied. "I would put that to the American people and say, what is your priority? Protecting thousands and hundreds of thousands and millions of people from a nuclear threat or bringing one journalist home? I'm not saying that you shouldn't be arguing for that one journalist, but there was a focus on a nuclear agreement that protects people for generations. I would say that is the highest priority."

Stengel identified an unspoken reality underlying all US foreign policy, regardless of who's in charge or what their worldview may be: Not all goals are of equal importance, and the US's leverage is never infinite.

Given this limited leverage, policy loses all focus unless certain objectives are prioritized ahead of others - or even sacrificed in favor of goals that are deemed particularly urgent. And in this case, the view was that the fate of one US citizen was less important than nuclear-arms control.

But Scarborough countered and said that seemingly competing objectives can't be separated as neatly as Stengel seems to think.

Since the nuclear deal was signed in July, Iran has tested a nuclear-capable ballistic missile in violation of a UN Security Council resolution, freed high-ranking al Qaeda prisoners (including the former interim head of the global terrorism network), arrested American-Iranian businessman Siamak Namazi, and convicted and sentenced Rezaian in a secret court.

These developments suggest there's a powerful hardline faction in Iran that's capable of pursuing a confrontational policy with the US even in spite of the nuclear deal - something that itself calls into question whether there's enough trust between the sides to sustain a complex and non-binding arms-control agreement over the course of several decades.

Stengel perhaps didn't intend to do this, but he bluntly illustrated the trade offs in the US's Iran policy. If you're going to prioritize arms control above everything else, then it stands to reason that press freedom - and even the freedom and protection of US citizens - is secondary to other, supposedly higher concerns.

Taken one way, Stengel is giving opponents of the US a recipe for getting a relatively free pass on both human rights and the harassment of American citizens. But he's also admitting that there are unsavory trade offs at the heart of the Obama administration's biggest foreign policy accomplishment.

Watch the segment here.