Transcript for Trump calls chemical attack in Syria 'an affront to humanity'

Good evening. It's great to have you with us on a Wednesday night. We begin tonight with president trump in there front of the world on Syria, on bashar Al Assad. On the apparent chemical attack that killed dozens in Syria. Calling it quote, a affront to humanity. Saying his attitude toward Syria has changed very much. More than 80 men, women and children dying. Those who did survive gasps for air. What the world was waiting for next, word from president trump. ABC's chief white house correspondent Jonathan Karl leading us off. Reporter: Welcoming the king of Jordan to the white house, the president firmly condemned the chemical weapons attack in Syria, placing the blaming squarely on the Syrian government. It is a terrible affront to humanity, I can tell you, terrible. Reporter: And later at a joint press conference in the rose garden, he suggested there should be retaliation. These heinous actions by the Assad regime cannot be tolerated. Reporter: In the past, again and again, Donald Trump said the U.S. Should not get involved. Tweeting "Syria is not our problem" when president Obama proposed protecting civilians. And after Assad's massive chemical weapons attack in 2013, he tweeted "Do not attack Syria, fix U.S.A." Adding, "If you do many bad things will happen & from that fight the U.S. Gets nothing!" But now, the president says these horrific images have changed his mind about the Assad regime. Innocent civilians suffering from this week's attack, more than 80 dead. Here a father clutches his twin 9-month-old babies, both killed -- I do change. And I am flexible. And I'm proud of that flexibility. And I will tell you, that attack on children yesterday, had a big impact on me. Big impact. And it's very, very possible, and I will tell you, it's already happened, that my attitude towards Syria and Assad has changed very much. Reporter: Trump blames president Obama for the humanitarian crisis but acknowledges it's now his challenge to solve. I now have responsibility and I will have that responsibility and carry it very proudly, I will tell you that. It is now my responsibility. I could just quickly ask you if the chemical attacks crosses a red line for you? It crossed a lot of lines for me. When you kill innocent children, innocent babies -- babies, little babies -- with a chemical gas that is so lethal. People were shocked to hear what gas it was, that crosses many, many lines, beyond a red line. Many, many lines. Reporter: But he gave no indication of what he may do. Well, one of the things I think you've noticed about me is 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. But I'm certainly not going to be telling you. Reporter: Today, king Abdullah made it clear, the world is looking to president trump. I believe under your leadership we will be able to unravel this very complicated situation. Reporter: And the president, while again blaming his predecessor, is promising to take action. The world is a mess. I inherited a mess. We're going to fix it. We're going to fix it. Jon Karl with us live at the white house. The president made it clear he won't say what he's going to do. Any kind of time line for possible action here sf. White house officials say this is very high on the agenda. In fact, the president himself chaired a meeting of his national security council today here at the white house on the chemical weapons attack. No time line yet for a response. We just heard president trump say that Syria crossed a red line, but several lines. Nikki Haley holding up pictures today if the U.N. Doesn't act the U.S. May have to. How many children have to die before Russia cares? The United States sees yesterday's attack as a disgrace at the highest level. Assurance that humanity means nothing to the Syrian government. When the united nations fails to act consistently, there are times where we are compelled to take our own action. I want to bring in Martha Raddatz with us tonight. You heard the president saying his attitude toward Syria has changed. We heard ambassador Haley say, at times we're compelled to take our own action. For Americans at home wondering what's going happen, what's next. What's the goal here? Do they want to prevent further attacks? Do they want to punish or get rid of bashar Al Assad? We don't know. Most of those chemical weapons, the stock piles are gone so the chemical weapons used here were hidden. This is much more difficult. As we heard, they met with the nation mall security team today all of this playing out

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