At a Senate Foreign Relations Committee hearing Thursday on Kerry's nomination to succeed outgoing Secretary of State Hillary Clinton, Kerry -- who currently serves as chairman of the committee -- told colleagues Washington has "extraordinary interests" in non-proliferation of nuclear weapons.
"The president has made it definitive. We will do what we must do to prevent Iran from obtaining a nuclear weapon," Kerry told the panel, "and I repeat here today, our policy is not containment. It is prevention, and the clock is ticking on our efforts to secure responsible compliance."
Kerry, a Massachusetts Democrat, said the administration, "working with Congress and an unprecedented international coalition, has put into place crippling sanctions on Iran. ... President Obama has stated again and again, and I want to emphasize this. He and I prefer a diplomatic resolution to this challenge, and I will work to give diplomacy every effort to succeed, but no one should mistake our resolve to reduce the nuclear threat."
Under questioning from Sen. Marco Rubio, R-Fla., who pressed for a more active U.S. role in global trouble sports, Kerry said: "We cannot afford a diplomacy that is defined by troops or drones or confrontation. We have to find a diplomacy that achieves ... understanding, rapprochement, whatever you want to call it."
Kerry rejected cutting off funding to U.N. agencies that take unilateral actions to recognize a Palestinian state, saying the United States would be more effective if it fully participates in funding.
On the Syrian civil war, Kerry said, "We need to change [Syrian leader] Bashar Assad's calculation" that he can win. "The goal ... is to effect some kind of orderly transition."
He said Obama understands the United States must keep a counter-terrorism initiative alive in Afghanistan once combat troops are removed next year, and help ensure a credible election in that country.
In a nod to the partisan divide in Washington, Kerry said, "If confirmed, I will invite all members of the committee to come together to talk about how we can have constructive dialogue in a collegiate atmosphere."
In statements before the committee Thursday, Clinton and Sen. John McCain, R-Ariz., endorsed Kerry.
"I know he will acquit himself in that office with distinction ... I commend his nomination to you without reservation," McCain told the committee.
McCain, who clashed with Clinton in her appearance before the committee Wednesday, praised Kerry at length for his efforts to normalize relations with Vietnam, though he recognized their political differences.
McCain and Kerry are decorated Vietnam veterans.
But later in questioning from the panel, McCain again asserted the U.S. public was "misled" about the attack in Benghazi.
"We still haven't gotten the answers about what happened at Benghazi.... There are some of us that won't give up on this, in spite of what some are saying in the media," he said.
Clinton, sitting next to McCain before the questioning of Kerry, told the panel: "John is the right choice to carry forward the Obama administration's foreign policy. ... He will bring a record of leadership and service that is exemplary."
Clinton was pummeled Wednesday by committee Republicans for actions before and after the Sept. 11, 2012, terror attack on the consulate in Benghazi, Libya, that killed the U.S. ambassador and three other Americans.
Kerry "is committed to doing whatever it takes to prevent other attacks and protect our people in posts around the world," Clinton said.
Kerry faced much more friendly questioning as he seeks to succeed Clinton at the State Department.
Before questions from the panel, Sen. Bob Corker, R-Tenn., ranking member on the Foreign Relations Committee, praised Kerry in his opening statement, saying, "You're ready to go. ... I think you know you're inheriting a department that is facing a number of challenges ... [in] a dangerous world."
During questioning, Corker tried to prod Kerry into criticism of former Sen. Chuck Hagel, R-Neb., who is Obama's choice to become secretary of defense. Corker pointed to Hagel's link to Global Zero, the international initiative to get rid of all nuclear weapons.
Corker didn't name Hagel, but referred to him as "this person."
Kerry said, "I believe in [nuclear] deterrence," but even past Republican secretaries of state have endorsed zero nuclear weapons as some future goal. Kerry said that goal would be far off.
But he said Hagel's stance has been distorted. "I think Sen. Hagel is realistic about it," Kerry said.
"I know Chuck Hagel and I think he is a strong patriotic former senator, and he will be a strong secretary of defense." Kerry said.
Kerry told Sen. Barbara Boxer, D-Calif., he would continue Clinton's efforts to advance women, particularly in negotiations with the Taliban in Afghanistan.
Responding to some joking references about his rooting for the Boston Red Sox and the New England Patriots, Kerry said, "If the standard here is about which teams I root for, I'm screwed."