Transcript for Chemical weapons confirmed to be dropped by Syrian military aircraft

We begin with fast-moving developments on sir wra. Just 24 hours after president trump said his mind had been changed on Syria, on bashar Al Assad. Tod today, he said something should happen. Dozens killed by Turkish officials now say was Saran gas. The survivors sprayed down. Many of the victims struggling to breathe. Tonight, we know that the defense secretary is now briefing the president on the options. What are they? And how soon could this come? ABC's chief global affairs correspondent Martha Raddatz leading us off. Reporter: Tonight, president trump, with his strongest words yet on the crisis in Syria. As this president, now 77 days into his presidency, decides whether to take military action. I think what Assad did is terrible. I think what happened in Syria is one of the truly egregious crimes. And it shouldn't have happened. And it shouldn't be allowed to happen. Have you talked to the Russian president about what happened? At some point I may. I haven't, but at some point I may. Do you think that Assad should leave power in Syria? I think what happened in Syria is a disgrace to humanity. And he's there and I guess he's running things, so something should happen. Reporter: The president's secretary of state, Rex tillerson, a man of few words since taking office, tonight with his strongest signal yet, focusing on Syria's president. Sir, does Assad have to go? Assad's role in the future is uncertain. Clearly, and with the act he has taken, it would seem there is no role for him to govern the Syrian people. Will you and president trump organize an international coalition to remove Assad? Those steps are under way. Reporter: But it was just one week ago, the secretary of state suggested something far different, saying the Syrian people should decide whether to get rid of Assad. This shift comes just 24 hours after the president, with the world watching, said those images of children gassed had changed his mind. I will tell you, it's already happened that my attitude toward Syria and aasad has changed very much. I'm not saying I'm doing anything one way or the other, but I'm certainly not going to be telling you. Reporter: Before he was president, Donald Trump had long argued against action in Syria, repeatedly tweeting about it. Back in 2013, after a chemical weapons attack then, when president Obama was weighing military action, trump tweeting, "Do not attack Syria. If you do, many bad things will happen. And from that fight, the U.S. Gets nothing!" Tonight, he is signaling his stance has changed. And the Russians, who have been supporting Syrian leader bashar Al Assad, said today support for Assad not unconditional, but urging caution. On capitol hill, a leading Republican said this is a test for trump. President trump has to make a decision that's going to define his presidency one way or another. If he does nothing it's going to be Obama on steroids. Reporter: The president hasn't said what he would do in Syria. But there are many military options. Hit Syrian airfields to ground Assad. What could we use? Sea-based cruise missile or u.s.-manned aircraft. Riskier but we have highly sophisticated war planes. Martha joins us me now. The president is being briefed on several options. They say it was an aircraft. They could go back and see what kind of aircraft dropped those missions. Martha as you been reporting we have more American troops there in recent weeks, we learned of hundreds more being sent into Syria. David, that's real concern. If military action is taken there will be a warning to Assad don't go anywhere near American troops, do not target them. But there's a risk. Martha, thank you. As you heard Martha if any

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