"It matters because a lot of other countries, whose policy has challenged these international norms, are watching," he said, specifically calling out North Korea and Iran, as well as terrorist organizations like Hezbollah. "They are watching. They want to see whether the United States and our friends mean what we say."
Mr. Obama similarly said the U.S. is considering a "limited, narrow act that would help make sure that not only Syria but others around the world understand that the international community cares about maintaining this chemical weapons ban and norm." Not responding, he said, "increases the risk that chemical weapons will be used in the future and fall into the hands of terrorists who might use them against us."
Kerry also said a response matters because of "who we are" as a nation, in spite of the current disinterest in becoming embroiled in another conflict.
"We know that after a decade of conflict, the American people are tired of war. Believe me, I am, too," he said. "But fatigue does not absolve us of our responsibility... And history would judge us all extraordinarily harshly if we turned a blind eye to a dictator's wanton use of weapons of mass destruction against all warnings, against all common understanding of decency, these things we do know."
If Mr. Obama decides to launch a military strike, he would most likely have to do it without the support of the United Nations and perhaps without backing from some of the United States' biggest allies. The British Parliament on Thursdayvoted against endorsing military action in Syria, all but assuring Britain would play no direct role in any U.S. attack. French President Francois Hollande, however, said Friday that France could still intervene militarily.
Kerry said America "should feel confident and gratified that we are not alone in our condemnation and we are not alone in our will to do something about it and to act." He cited supportive remarks from France, the Arab League, the Organization for Islamic Cooperation, Turkey and Australia. United Nations inspectors are still investigating the Aug. 21 chemical weapons attack in the suburbs of Damascus but are expected to finish their probe on Friday and leave Syria on Saturday. Kerry noted that the U.N. does not intend say in its report who was responsible for the chemical attacks.
A poll released Friday shows that half of Americans oppose taking military action in Syria, even in response to the use of chemical weapons. Fifty percent of Americans oppose military action, according to the NBC poll conducted August 28-29, while 42 percent support it. Most Americans -- 79 percent -- say Mr. Obama needs to receive congressional approval before taking any military action.
Congress isn't set to return from its summer recess until the Sept. 9, but the administration has consulted with the legislative branch. High-level administration officials on Thursday evening held a conference call with congressional leaders aimed at updating lawmakers on the situation and soliciting their views on possible military action. A number of members of Congress said after the call that the U.S. cannot stand by while the Assad regime allegedly uses chemical weapons.
Thursday's "briefing reaffirmed for me that a decisive and consequential U.S. response is justified and warranted to protect Syrians, as well as to send a global message that chemical weapons attacks in violation of international law will not stand," Sen. Robert Menendez, D-N.J., chairman Senate Foreign Relations Committee, said in a statement.
Sen. Bob Corker, R-Tenn., the top Republican on the Foreign Relations Committee, said in a statement, "While I'm opposed to American boots on the ground in Syria, I would support surgical, proportional military strikes given the strong evidence of the Assad regime's continued use of chemical warfare."
He also said the administration would be "better off" seeking congressional authorization to use force, "which would provide the kind of public debate and legitimacy that can only come from Congress."
Some other members of Congress have stated their opposition to any military action at this point. Rep. Tammy Duckworth, D-Ill., a war veteran who lost both of her legs in Iraq, said in a statement, "Until I feel it's imperative to our national security, I will not support preemptive intervention in Syria."
Sen. Rand Paul, R-Ky., said on Fox News on Thursday, "I will do everything I can to stop the president. We should not engage in a war, and we shouldn't engage in it in an unconstitutional fashion."