U.S. sailors' release: Diplomatic coup or cowing to Iran?

But Obama's opponents argued that the sailors should never have been detained in the first place by the Iranian Revolutionary Guard Corps (IGRC) and painted the episode as yet another example of belligerent Iranian behavior that had only been encouraged by a softer U.S. stance towards Tehran.

Fury has been mounting among Republicans after the video's release, which also showed a naval officer apologizing for straying into Iranian territorial waters.

"They never should have been taken into custody," Arizona Republican Sen. John McCain told CNN's Manu Raju.

"Look at this picture," McCain said, holding up a copy of the Wall Street Journal that featured a still of the video across the front page.

"This is really another embarrassing moment and a great propaganda victory for the Iranians," said McCain, a former Vietnam War prisoner who is now chairman of the Senate Armed Services Committee.

"They are now taking our American servicemen, putting them on their knees, taking off their shoes, and having them hold their hands above their head," continued McCain, himself a former naval officer. "That's not the way the United States would have been treated under any other president that I know of."

Florida Sen. Marco Rubio, who is seeking the Republican nomination for president, also registered outrage at the treatment of the sailors.

"They took pictures of them and video and put it up on Iranian television as to say, 'Look at what we can do to America. We can capture their sailors and we can make them get on their knees, we can humiliate them," he said on Fox News' "On the Record with Greta Van Susteren."​

"Do you know why they did this? Because they know they can get away with it. Because they know Barack Obama is weak."

With the administration suddenly on the defensive, State Department spokesman John Kirby told CNN's Jake Tapper on "The Lead" that the videos were "hard to look at" but urged critics to concentrate on the fact that the sailors were returned quickly.

"What we are most happy about here in the State Department is that we were able to get them home in less than 24 hours, (with) 10 fingers, 10 toes, nobody hurt. They are all safe and we got our boats back, and I think that is the most important thing."

White House spokesman Josh Earnest told reporters, meanwhile, that the President had seen the pictures of the American sailors with their hands on their heads and expected to get a full briefing on the incident.

In a few tense hours on Tuesday, the crisis had threatened to prove a major political embarrassment for Obama, particularly since the sailors were being held while he delivered his final State of the Union address. He didn't mention the captives while he was speaking, instead highlighting the Iran nuclear deal as a top legacy achievement.

Pressed into crisis mode, Secretary of State John Kerry led U.S. diplomacy to free the sailors. He spoke five times by telephone to Iranian Foreign Minister Mohammad Javad Zarif, with whom he bonded during tortuous negotiations last year over the nuclear deal.

Kerry told Zarif that "if we are able to do this in the right way, we can make this into what will be a good story for both of us," a senior State Department official told reporter.

With the crisis resolved, Kerry thanked Iran on Wednesday and chalked up a victory for the administration.

"In fact, it is clear that today, this kind of issue was able to be peacefully resolved and efficiently resolved and that is a testament to the critical role that diplomacy plays in keeping our country safe and strong," he said.

On Air Force One on Tuesday, Obama spokesman Josh Earnest said that the President's decision not to raise the issue during the speech -- despite demands from hawkish Republicans -- to avoid upsetting delicate diplomacy had helped resolve the crisis.

There was precedent for such a standoff to further deteriorate. Back in 2007, Iran held 15 British sailors and Marines and accused them of trespassing in its territorial waters. In an acute embarrassment for the British government, the service members were paraded before then-President Mahmoud Ahmadinejad and critics said their apologies were extracted under duress.

It is partly the knowledge of past Iranian behavior that has skeptics doubting the administration's claim of a diplomatic victory, especially at the time when Tehran is projecting its power throughout the region and worrying U.S allies.

Critics pointed out that with Iran set to get more than $100 billion in sanctions relief with the implementation of the nuclear deal, Tehran had plenty of incentives other than succumbing to American diplomatic pressure to bring the standoff to a quick resolution.

"What's remarkable to me is with $100 billion-plus imminent, the Iranians continue to act with impunity in provoking the administration," said Mark Dubowitz, a sanctions expert with the Foundation for Defense of Democracies.

Such provocations include recent ballistic missile tests that the U.N. says infringed a Security Council resolution, the holding of several Americans inside Iran, close calls with the U.S Navy in the Persian Gulf, intensification of the proxy war against Saudi Arabia and a doubling down of support for Syrian leader Bashar al-Assad.

The State Department has insisted that Kerry did not deliver an official apology for the actions of the sailors, who were traveling in two small coastal launches and strayed into Iranian waters in Farsi Island in the Persian Gulf.

Despite the video and the sailor's apology, officials in Washington were hopeful that the way that the situation was resolved could pave the way for less confrontational relations with Tehran in the future and perhaps provide a model for talks on the freeing of American prisoners in Iran.

"In terms of what impact this will have on other things or whether it gives greater confidence about anything else, I think it's too soon to make an assessment like that," the senior State Department official said.

But in a tweet, Zarif expressed a similar hope that future clashes could be solved in a comparably effective way.

"Happy to see dialog and respect, not threats and impetuousness, swiftly resolved the #sailors episode. Let's learn from this latest example," he said.

However, Iranian internal politics are notoriously opaque and it would not be surprising if the capture of the sailors was a symptom of power struggles within the country. Political tensions are acute in the run-up to crucial elections next month for the country's parliament, the Majlis, and a powerful body called the Assembly of Experts that has the power to appoint the Supreme leader.

The IRGC has been much more critical of the nuclear deal than the political leadership, and some see this incident as an effort to assert their authority.

A desire to avoid embarrassing Zarif and President Hassan Rouhani and to provide ammunition to hardline opponents of the nuclear deal may be one reason why the U.S. administration has yet to impose promised sanctions over the missile tests.

"What happened with the sailors, to me, is an indication that the Revolutionary Guards are sending a message to Obama and to Rouhani that they are in charge," Dubowitz said.

"The deal may have been negotiated with Rouhani and Zarif, but it will be the Revolutionary Guards who will dictate the terms and dictate the implementation."

Under this interpretation of the events in the Persian Gulf, the IRGC made their point at a critical moment before Obama's State of the Union and had no need to overplay their hand by keeping the sailors.

And steeped in Iranian business dealings, they personally have much to gain by the easing of sanctions to take place if the nuclear deal's implementation goes ahead as planned.