JUDY WOODRUFF: This week's chemical attack in Northern Syria has now claimed 75 lives, and it may trigger a shift in U.S. policy.
The president today voiced his outrage and threatened a tougher approach.
John Yang begins our coverage.
PRESIDENT DONALD TRUMP: These heinous actions by the Assad regime cannot be tolerated.
JOHN YANG: At a Rose Garden news conference with King Abdullah of Jordan, President Trump condemned the attack as an affront to humanity.
PRESIDENT DONALD TRUMP: When you kill innocent children, innocent babies, babies, little babies, with a chemical gas that is so lethal, and people were shocked to hear what gas it was, that crosses many, many lines, beyond a red lines, many, many lines.
And I will tell you, it's already happened, that my attitude toward Syria and Assad has changed very much.
JOHN YANG: Administration officials had been saying that removing Syrian President Bashar al-Assad was no longer a fundamental option.
But, today, Mr. Trump didn't seem to rule anything out.
Last year, you seemed to be reluctant to get involved or to intervene in Syria directly. Is that one thing that's changed after yesterday?
PRESIDENT DONALD TRUMP: Militarily, I don't like to say where I'm going and what I'm doing. I'm not saying I'm doing anything, one way or the other.
JOHN YANG: The U.N. Security Council held an emergency session, but took no action.
U.S. Ambassador Nikki Haley warned that the United States will act if no one else does.
NIKKI HALEY, U.S. Ambassador to the United Nations: When the United Nations consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action.
JOHN YANG: The Syrians continued to deny they launch any chemical attack, and its ally Russia called the reports fake information.
Haley charged that Moscow especially has made an unconscionable choice.
NIKKI HALEY: They chose to close their eyes to the barbarity. They defied the conscience of the world. How many more children have to die before Russia cares?
JOHN YANG: Meanwhile, victims of the attack continued to pour into hospitals in Syria's Idlib province and in nearby Turkey.
WOMAN (through interpreter): There was a lot of smoke, and there was a smell. It was very difficult to breath. We couldn't breathe anymore. We just couldn't breathe anymore.
JOHN YANG: The World Health Organization said the symptoms are consistent with a nerve agent. Doctors Without Borders said it could have been sarin, the same agent used in a deadly 2013 attack outside Damascus.
Both today and yesterday, President Trump was highly critical of Barack Obama, saying that he failed to deal with Assad by backing off the threat of military force. Now President Trump says the responsibility of dealing with Assad is his — Judy.
JUDY WOODRUFF: Thank you, John, at the White House.