Secretary of State John F. Kerry appeared on “Face The Nation,” where he discussed the recent diplomatic nuclear deal with Iran. (REUTERS)

Secretary of State John F. Kerry was a man in his element in Sunday’s pre-dawn hours, when he announced details of a historic diplomatic agreement with Iran. Nearly all the roles he has played in a long career in public life came into view.

There was the pragmatic deal-cutting senator of nearly three decades — the experience that most defines Kerry’s approach to his new executive-branch job as chief diplomat.

The i-dotting lawyer was there, too, as was a little of the jaded war veteran and the ambitious politician who once sought but fell short of the presidency.

The deal Kerry was instrumental in cutting is a diplomatic coup, even if its effectiveness and durability remain in doubt. It sets new boundaries for Iran’s disputed nuclear program that represent significant compromises and concessions for Iran as well as the international coalition that suspects it of seeking nuclear weapons.

Perhaps more important, the agreement opens a crack in the hostility and suspicion hardened over more than 30 years of American diplomatic estrangement from Iran.

Iran agrees to limit uranium enrichment

“This has been a difficult and a prolonged process,” Kerry said in announcing terms of the deal, which is opposed by Israel and deeply unpopular among a bipartisan swath of Kerry’s former congressional colleagues.

“It’s been difficult for us, and it’s been difficult for our allies, and it’s obviously been difficult for the government of Iran,” Kerry continued, warning that the agreement is only a six-month, confidence-building interim. The hard work of a permanent deal is still ahead, Kerry said.

The agreement, signed at 3 a.m. Sunday, was the work of many lesser-known diplomats, including Wendy Sherman, the State Department’s undersecretary for political affairs and its representative to the negotiations over Iran’s nuclear program. But Kerry’s admirers and critics both credit his tenacity and his game, give-it-a-shot style.

British Foreign Secretary William Hague praised Kerry’s efforts Sunday, and the two joked about their mutual lack of sleep.

“I particularly want to pay tribute to the work of Secretary Kerry, who has been so determined throughout the negotiations with Iran to make sure that this is a robust deal, that everything that should be covered is covered and that every commitment that we wanted from Iran is as strong as it should be,” Hague said in London. “And he has done that, and I really pay tribute to his persistence and his leadership in doing that.”

Kerry flew overnight Friday to join the Iran talks that went into overtime Saturday. He went directly into back-to-back strategy sessions with foreign ministers of the other world powers trying to broker a deal and also bargained directly with Iranian Foreign Minister Mohammad Javad Zarif.

“This is a partnership effort. No one country can do this,” Kerry said in London later Sunday. “The P5+1 were unified, and we all came together in consultation with a lot of effort together,” he added, glossing over differences among the six-nation bargaining bloc that contributed to a breakdown in the Iran talks two weeks ago.

When the same fate appeared possible or likely Saturday evening, it was Kerry’s stock that stood to fall furthest, because he had the most invested.

“From the outside, Kerry looks like he played the role of an effective closer,” said Jon Alterman, director of the Middle East program at the Center for Strategic and International Studies. He stressed that Kerry’s performance cannot be fully measured now, because the ins and outs of the closed-door talks remain largely secret.

Kerry has seemed relentless on any number of foreign policy crises in recent months. Alongside direct talks with Iran this fall, Kerry bargained one on one with Russian Foreign Minister Sergei Lavrov and then with the U.N. Security Council to win a deal to destroy Syria’s chemical weapons. He appeared unannounced in Kabul last month to try to salvage stalled security talks, and he kept up direct pressure on Israel and the Palestinians to continue peace talks he had invested months in starting.

That unyielding ambition has opened Kerry to criticism that he is attempting to resolve crises even where there is little chance of success.

The much-anticipated peace conference that could end the Syrian civil war has been postponed repeatedly because of disarray among the U.S.-backed opponents of Syrian President Bashar al-Assad (The United Nations announced Monday morning that the conference would be held on Jan. 22). Israeli-Palestinian peace talks are currently in flux too, after a walkout by Palestinian negotiators. In Afghanistan, weeks after Kerry reached a tentative agreement with President Hamid Karzai on a long-term security framework, Karzai is declining to sign it.

Still, more than other recent secretaries of state, Kerry is willing and apparently eager to intervene personally in crises and implacable problems, and to do it all at once. There is little of the caution that defined immediate predecessor Hillary Rodham Clinton or the reserve and formality of Condoleezza Rice.

He has confidence in his ability to lobby the U.S. case in person — risky business if it goes wrong. Kerry often sounds like the foreign policy troubleshooter he was when, as a senator from Massachusetts, he was deployed by President Obama to calm crises in Afghanistan and elsewhere.

Kerry “believes in personal diplomacy, believes that face-to-face negotiations are effective,” State Department spokeswoman Jen Psaki said before Kerry joined the talks in progress Saturday. “I don’t think he would mind hopping on the plane to fly to Geneva if that’s a step that makes sense.”