In his weekly radio and Internet address, the president said the United States "has presented a powerful case to the world that the Syrian government was responsible for this horrific attack on its own people."
"This was not only a direct attack on human dignity; it is a serious threat to our national security," he said. "There's a reason governments representing 98 percent of the world's people have agreed to ban the use of chemical weapons. Not only because they cause death and destruction in the most indiscriminate and inhumane way possible -- but because they can also fall into the hands of terrorist groups who wish to do us harm.
"That's why, last weekend, I announced that, as commander in chief, I decided that the United States should take military action against the Syrian regime," Obama said.
The president said the United States will "be stronger if we act together, and our actions will be more effective. That's why I asked members of Congress to debate this issue and vote on authorizing the use of force."
As he had said several times this week, the president said whatever action he takes will not be "an open-ended intervention. This would not be another Iraq or Afghanistan. There would be no American boots on the ground. Any action we take would be limited, both in time and scope -- designed to deter the Syrian government from gassing its own people again and degrade its ability to do so."
"I know that the American people are weary after a decade of war, even as the war in Iraq has ended, and the war in Afghanistan is winding down," he said. "That's why we're not putting our troops in the middle of somebody else's war.
"But we are the United States of America. We cannot turn a blind eye to images like the ones we've seen out of Syria. Failing to respond to this outrageous attack would increase the risk that chemical weapons could be used again; that they would fall into the hands of terrorists who might use them against us, and it would send a horrible signal to other nations that there would be no consequences for their use of these weapons. All of which would pose a serious threat to our national security."