Secretary of State John Kerry predicted this morning on "This Week" that Congress will authorize the president to order a military strike on Syria as punishment for the country's alleged use of chemical weapons against its civilian population last month.

"We are not going to lose this vote," Kerry said of the coming debate to authorize military action against Syria when Congress returns from recess. "The president of the United States is committed to securing the unity of purpose that he believes strengthens America. And I believe the Congress will see that that's the responsible thing to do here."

Speaking from the Rose Garden at the White House Saturday, President Obama said that although he believed he had the authority to order an attack on Syria without the authorization of Congress, he had decided to seek their consent before ordering any such strike on the regime of Bashar al-Assad.

ABC's Jon Karl reported earlier Sunday that according to a senior House Republican, a vote to authorize a strike against Syria would fail if it happened today.

During the interview, Secretary of State Kerry also responded to declarations of victory from the Assad regime.

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"Assad has said a lot of things in the course of this that I think the more he stands up and crows, the more he will help this decision to be made correctly," Kerry told ABC's George Stephanopoulos.

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Kerry also offered more specific details about evidence the U.S. has pointing to the use of the chemical weapon Sarin in Syria.

"We now have evidence from hair and blood samples from first responders in East Damascus, the people who came to help, we have signatures of Sarin in their hair and blood samples, so the case is growing stronger by the day," Kerry said.

"I believe that as we go forward here in the next days, the Congress will recognize that we cannot allow Assad to be able to gas people with impunity," he added.

Kerry said earlier this week that the alleged chemical weapon attack killed almost 1,500 people, including more than 400 children.

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