For the world, a controversial deal cut Sunday could mean a pause of six months or longer in Iran's nuclear program. For Iran, it could mean $7 billion in relief from crippling economic sanctions.
For John Kerry, it could represent the apex of a political career spanning decades, including a long Senate career, four years as chairman of the powerful Senate Foreign Relations Committee and 10 months as secretary of State.
The agreement, Kerry said Sunday, "impedes the progress in a very dramatic way of Iran's principal enrichment facilities and parts of its program and ensures they cannot advance in a way that will threaten our friends in the region, threaten other countries, threaten the world."
The current chairman of the Senate Foreign Relations Committee is among a growing number of leaders on both sides of the aisle who say they aren't so sure.
"In my view, this agreement did not proportionately reduce Iran's nuclear program for the relief it is receiving," Sen. Robert Menendez, D-N.J., said in a statement. "Given Iran's history of duplicity, it will demand ongoing, on-the-ground verification."
"Kerry is certainly trying," writes Amy Davidson, a senior editor at The New Yorker. "And he appears to have managed to get his fingers on the edge of something that could be historic. Now the task is to not let go."
Kerry, 69, replaced Hillary Rodham Clinton in February after 28 years in the Senate, the last four of them as Foreign Relations chairman.
A Yale graduate, Kerry served in the Navy and served in combat as a Swift Boat skipper in Vietnam, earning a Silver Star, a Bronze Star with Combat V and three Purple Hearts. When he came home, he spoke out against the war, a position that became a point of controversy when he ran for president against George W. Bush in 2004.
In 2010, as Foreign Relations chairman, Kerry was instrumental in the ratification of the New START (Strategic Arms Reduction Treaty), a nuclear arms reduction agreement with Russia.
His short time with the State Department has been busy, including efforts to revive the Palestinian peace talks, a deal brokered with Russia aimed at removing chemical weapons from Syria, and a post-withdrawal security agreement with Afghanistan.
That "it's looking more and more possible that when the history of early-21st-century diplomacy gets written, it will be Kerry who is credited with making the State Department relevant again."