He wins praise from an illustrious Republican predecessor, George Shultz. "He is doing a terrific job," says Shultz, who served under President Ronald Reagan. "He has thought about this territory energetically and creatively for a long time."
There are caveats. Kerry's habit of periodically putting his foot in his mouth hasn't vanished. He hailed a long-term deal with Afghan President Hamid Karzai that hasn't yet materialized; his rhetoric on Syria was all over the lot; and he misspoke about leaders of Egypt's military coup.
It remains an open question whether the White House will try to rein him in. Associates say he and President Barack Obama respect each other, though accounts that they forged a close bond when Kerry helped prepare Obama for the debates against Mitt Romney during the last presidential campaign are exaggerated.
But this White House, more than any since Richard Nixon's, clings to power and authority. Even Secretary Clinton, despite her political standing, was kept on a bit of a leash.
And Susan Rice, the president's national security adviser, wanted to be secretary of state but removed herself from contention with her comments on the killing of U.S. diplomats in Libya.
She and Kerry share lunch periodically; the relationship, at best, is correct. A National Security Council review of Middle East policy didn't include the State Department, and the White House has imposed a number of top State Department officials.
Restraints or not, Kerry is a diplomatic risk-taker; the White House was delighted to give him the Israeli-Palestinian account, which was viewed as doomed. Progress has been minimal, but Kerry is relentless.
He is a lead figure in the tentative pact with Iran and will be central in selling the Iranians and Congress on any final deal. Much of his tenure has been consumed by the Middle East. An Asia trip is slated for this week that will include a stop in Vietnam. Kerry fought there in the 1960s, and in the 1980s and '90s, he led the move toward U.S. reconciliation with the southeast Asian nation.
He doesn't engender much goodwill in the State Department. This is left to Bill Burns, a deputy secretary and veteran diplomat; their relationship, by all accounts, is a good one. Reportedly, it was Burns who persuaded the secretary to tap a respected envoy, Martin Indyk, to work on the Israeli- Palestinian negotiations.
Top White House aides still occasionally roll their eyes at the mention of Kerry, though there's also a grudging respect now. Shultz says the key to Kerry's success will be his relationship with the president: "They weren't on the same page on Syria, and that was embarrassing. But if John's skills and knowledge are appreciated, he and the president can get together to work out strategies."
Some Kerry initiatives could backfire, and the White House will tighten the leash. Perhaps Team Obama learned a painful lesson from the disastrous rollout of the Patient Protection and Affordable Care Act - a casualty, in no small part, of White House insularity.
If he succeeds, Kerry's career will have come full circle, from decorated combat veteran to anti-war activist to diplomat extraordinaire.