Kerry, Defense Secretary Chuck Hagel and Joint Chiefs of Staff Chairman Martin Dempsey testified Tuesday before the Senate Foreign Relations Committee on the use of force in Syria in response to intelligence reports that chemical weapons were used Aug. 21 in Damascus suburbs, killing 1,400 people.
Although Congress doesn't officially return to Washington until next week, many of the relevant committees are meeting this week on President Obama's authorization request.
Kerry said evidence indicated "not one rocket landed in regime-controlled territory, not one. All of them landed in opposition-controlled or contested territory. ... We are certain that none of the opposition has the weapons or capacity to effect a strike of this scale.
That Assad's regime carried out the worst chemical weapons attack of the 21st century "is beyond question," Kerry said.
"This debate is about the world's red line, about humanity's red line," Kerry said. "A line that anyone with a conscience should draw.
"Now, some people here and there, amazingly, have questioned the evidence of this assault on conscience. I repeat here again today that only the most willful desire to avoid reality can assert that this did not occur as described or that the regime did not do it. It did happen. And the Assad regime did it."
Not wanting a repeat of Iraq, where claims of weapons of mass destruction were used to justify the toppling of Saddam Hussein's regime only to be proven groundless later, Kerry said the intelligence community "scrubbed and rescrubbed" the evidence it received from Syria.
Obama has asked Congress for authorization to degrade and deter Assad's capacity to use chemical weapons, the nation's top diplomat said. No one is asking America to go to war or put American boots on the ground, Kerry stressed.
"Forcing Assad to change his calculation about his ability to act with impunity can contribute to his realization that he cannot gas or shoot his way out of his predicament," Kerry said. "And as I think you know, it has been the president's primary goal to achieve a negotiated resolution, but you [have] got to have parties prepared to negotiate to achieve that.
"We need to send to Syria and to the world, to dictators and to terrorists, to allies and to civilians alike the unmistakable message that when the United States of America and the world say, never again, we do not mean sometimes.
"We do not mean the somewhere. Never means never."
A protester shouted, "We don't want another war. Nobody wants this war," after Kerry finished and before Hagel spoke.
Hagel said he and Dempsey both assured Obama that U.S. forces will be ready if Obama gives the order.
"The Department of Defense has developed military options to achieve these objectives, and we have positioned U.S. assets throughout the region to successfully execute this mission," Hagel said. "We believe we can achieve them with a military action that would be limited in duration and scope."
Hagel said chemical weapon use in Syria not only was an assault on humanity but also a serious threat to America's national security interests and U.S. allies.
"The Syrian regime's use of chemical weapons poses grave risk to friends and partners along at Syria's border, including Israel, Jordan, Turkey, Lebanon and Iraq," Hagel said. "If Assad is prepared to use chemical weapons against his own people, we have to be concerned that terrorist groups like Hezbollah, which has forces in Syria supporting the Assad regime, would acquire them and would use them."
Hagel said the military action would be tailored to respond only to the use of chemical weapons.
"A political solution created by the Syrian people is the only way to ultimately end the violence in Syria," he said.
The defense secretary also said the United States was committed to do more to help the Syrian opposition.
In closing, Hagel said, "A refusal to act would undermine the credibility of America's other security commitments, including the president's commitment to prevent Iran from acquiring a nuclear weapon. The word of the United States must mean something."
"It is vital currency in foreign relations and international and allied commitments."
Before the hearing, Obama expressed appreciation that Congress has begun scheduling hearings and intends to vote soon on his authorization request.
"[We] have high confidence that Syria used in an indiscriminate fashion chemical weapons that killed thousands of people, including over 400 children, and in direct violation of the international norm against using chemical weapons," Obama said. "That poses a serious national security threat to the United States and to the region and, as a consequence, Assad and Syria need to be held accountable."
He stressed that the military plan developed by the Joint Chiefs of Staff is proportional, limited and doesn't involve boots on the ground.
"This is not Iraq, and this is not Afghanistan," Obama said. "This is a limited, proportional step that will send a clear message, not only to the Assad regime, but also to other countries that may be interested in testing some of these international norms that there are consequences."
While the action would provide the ability to degrade Assad's capabilities concerning chemical weapons, Obama said it also would fit into a broader strategy "to make sure that we can bring about over time the kind of strengthening of the opposition and the diplomatic and economic and political pressure required so that ultimately we have a transition that can bring peace and stability, not only to Syria, but to the region."