Sen. John McCain (R-Ariz.), center, and Senate Armed Services Committee Chairman Carl Levin (D-Mich.), right, rush to a closed-door briefing with intelligence officials about the Obama administration’s decision to swap five members of the Taliban for captive Army Sgt. Bowe Bergdahl. (J. Scott Applewhite/AP)

The Obama administration on Wednesday stepped up its efforts to defend its decision to free five Taliban commanders in exchange for the release of Army Sgt. Bowe Bergdahl, hoping to calm criticism from Capitol Hill and within military ranks.

Senior diplomats and intelligence officials involved in the negotiations, which culminated Saturday with Bergdahl’s release, delivered a classified briefing to all U.S. senators in a secure Capitol meeting room.

During the session, the officials showed senators, many of whom have been critical of the administration’s failure to notify Congress of the Taliban prisoner release, a proof-of-life video of Bergdahl recorded in December 2013.

People familiar with the briefing said that U.S. intelligence officials, including deputy director of national intelligence Robert Cardillo, pointed out evidence in the video of Bergdahl’s declining health, comparing his appearance with the last images of him from three years ago.

Senators leaving the briefing said that Bergdahl looked sickly in the video and that he stammered as he identified himself.

PostTV and Dan Lamothe of The Washington Post’s new Checkpoint blog point out key moments in the video released by the Taliban showing Sgt. Bowe Bergdahl's recovery. (Dan Lamothe and Sarah Parnass/The Washington Post)

“It did not look good,” Sen. Mark Kirk (R-Ill.) said about Bergdahl’s condition. “I would definitely think that it would have had an emotional impact on the president when he saw it.”

But other Republicans said that they were not satisfied with the answers they received at the briefing and that they remain concerned that the released Taliban members could return to the fight.

President Obama has said Bergdahl’s frail condition was one reason for the need to act quickly, at the cost of notifying Congress in the legally required time frame.

The questions surrounding improper congressional notification are one aspect of the Bergdahl case that has clouded the return of the longest-held prisoner of war of the post-Sept. 11, 2001, era. A moment that Obama celebrated Saturday in the White House Rose Garden — with Bergdahl’s parents by his side — has in recent days emerged as a challenge to the president’s judgment and management of delicate end-of-the-war issues.

Bergdahl left his small outpost in Afghanistan’s Paktika province in June 2009. Some of Bergdahl’s fellow soldiers have called his disappearance tantamount to desertion. The subsequent search for Bergdahl, which ranged over months in the volatile summer and fall of 2009, may have imperiled U.S. troops and stretched resources better used in other operations, according to some former military officials.

At a NATO defense ministers’ meeting in Brussels, Defense Secretary Chuck Hagel dismissed accusations Wednesday that the hunt for Bergdahl may have cost as many as eight U.S. troops their lives.

“I do not know of specific circumstances or details of U.S. soldiers dying as a result of efforts to find and rescue Sergeant Bergdahl,” Hagel said. “I am not aware of those specific details or any facts regarding that issue.”

Hagel reiterated that Bergdahl, now at a military hospital in Landstuhl, Germany, will be given time to recover before he is questioned about his disappearance. Military officials have said those circumstances will be investigated.

As administration officials in Washington sought to explain the Bergdahl exchange, the Taliban released a video of the soldier’s transfer, which occurred in the known Haqqani stronghold of Khost province.

In the clip, Bergdahl, dressed in traditional Afghan clothes, his head shaved, awaits a Black Hawk helicopter, surrounded by about 18 Taliban fighters. He is handed over to U.S. Special Operations forces, who pat him down for weapons and explosives before taking him away.

“Don’t come back to Afghanistan,” one of the Afghan men is heard saying to Bergdahl. “If you come back, you will not leave alive.”

The negotiations for Bergdahl’s release took shape in the early months of 2011 and evolved over the next three years into the agreement announced over the weekend.

When the talks began as part of what U.S. officials hoped would be a broader Afghan peace effort, U.S. envoys were forbidden to offer any detainees held in the military prison at Guantanamo Bay, Cuba, as part of a trade for Bergdahl. According to people familiar with the process, negotiators were allowed to include only Taliban fighters held at the detention center at Bagram air base, outside Kabul.

Those restrictions put Taliban moderates open to peace talks — including Tayeb Agha, who was appointed by Taliban leader Mohammad Omar to represent him in the negotiations — in a difficult position with the movement’s more hard-line elements.

As one person familiar with the discussions — who like others spoke on the condition of anonymity to describe the secret negotiations — said, Agha could not sell that deal.

The Taliban countered with a list of six senior Taliban officials being held at Guantanamo Bay. The list included the five Taliban commanders released as part of the Bergdahl agreement, as well as a sixth who died during the talks, which stretched from February 2011 until June 2012.

Among the negotiators were U.S. envoys, including at times Marc Grossman, the special representative for Afghanistan and Pakistan; a German diplomat; Qatari officials; and Agha. In Washington, initial resistance from many of those in Obama’s war cabinet faded into support in principle for a five-to-one swap.

Although the broad outline of the agreement was in place early, the talks got hung up over the staging of the release and the strength of the guarantees from the government of Qatar, which had agreed to take the released Taliban detainees.

U.S. negotiators proposed that Bergdahl be released at the same time two of the five Guantanamo detainees would be sent from the prison to Qatar, where they would face a travel ban to any destination outside the country. The three remaining detainees would be released three months later.

The Taliban wanted all five to be released at the same time as Bergdahl, with the stipulation that once in Qatar, they would be permitted to travel to Saudi Arabia for the annual pilgrimage to Mecca and to Europe, if necessary, for medical care. U.S. negotiators rejected those conditions.

From the beginning, then-national security adviser Thomas E. Donilon and his deputy, Denis McDonough, now the White House chief of staff, supported the five-for-one terms.

But nearly every other senior adviser to Obama, led by then-CIA Director Leon E. Panetta and then-Defense Secretary Robert M. Gates, opposed the exchange. So, too, did then-Secretary of State Hillary Rodham Clinton, now considering a run for president in 2016, who since Bergdahl’s release has expressed public support for the exchange.

Nick Merrill, a spokesman for Clinton, said Wednesday that “she set a high bar and insisted on strict conditions for any deal, but as she said this week, America has a noble tradition that we leave no soldier behind.”

“I think concern among some of these guys had to do with whether or not we could get a travel ban for the five in Qatar,” said a former senior administration official, who spoke on the condition of anonymity to describe the internal thinking at the time. “Once they got that travel ban, there was support.”

Senior advisers started moving faster toward the deal, as well, after Gates and Panetta left the administration. But officials said the Taliban still opposed the agreement, causing talks to drag on far longer than expected.

As this year began, Taliban officials came around, aware that the value of Bergdahl was declining as U.S. troops withdraw in advance of the official end of U.S. involvement in the war at the end of 2014.

A U.S. counterterrorism adviser said the Taliban was also feeling more military pressure. Specifically, the Haqqani network, the Taliban affiliate that was holding Bergdahl in Pakistan, was growing concerned.

The September 2013 killing of Badruddin Haqqani, the son of the elder Jalaluddin Haqqani, the network’s founder, in a U.S. drone strike provided an incentive for the network to start thinking seriously about releasing Bergdahl.

“If you can reach out and kill one of the immediate family members, then the whole network has to start thinking, ‘We have a problem,’ ” the adviser said. “There was probably a clock ticking on the other side.”

Two administration officials familiar with the discussions in recent weeks said there was fear that the Taliban, eager to unload a prisoner in poor health and of declining trade value, would kill Bergdahl if negotiations stalled again.

Administration officials have acknowledged that they did not notify Congress at least 30 days in advance of a Guantanamo detainee release, as required by the National Defense Authorization Act of 2014. There were concerns, officials said, that notifying Congress would lead to public disclosure of the operation or new political roadblocks that administration officials say could have killed the exchange and potentially imperiled Bergdahl.

Officials familiar with the final round of talks said the deal was reached far more quickly than expected. One official said a negotiating team arrived in Qatar about 21 / 2 weeks ago with a final proposal.

The expectation, the official said, was to present the terms and then leave Doha, the capital of Qatar, to await the Taliban response. But Qatari officials told U.S. negotiators to remain in the city, suggesting the Taliban planned to move quickly to secure the agreement.

To the surprise of the U.S. team, the agreement for the handover, including the time, place and details about who would attend, were worked out over about a week. Members of the U.S. team were in Doha as Bergdahl’s handover occurred, and they were still there when the five former detainees were flown in, the official said.

The U.S. officials had no direct contact with the Afghans.

Kevin Sieff in Kabul and Adam Goldman, Wesley Lowery and Paul Kane in Washington contributed to this report.