JUDY WOODRUFF:

As we reported earlier, President Trump said that the chemical weapons attack yesterday in Syria has crossed many lines for him. But what options could the president pursue in the six-year civil war?

I'm joined now by two experts with deep experience in military strategy and planning.

Andrew Exum was a deputy assistant secretary of defense for Middle East policy in the Obama administration. He's now a contributing editor at The Atlantic magazine. And Kori Schake, she was the director for defense strategy at the National Security Council during the George W. Bush administration.

And we welcome both of you to the program.

Kori Schake, to you first.

When the president said today — it was a striking comment. He said what happened with this chemical attack this week had caused him to completely rethink his attitude towards Syria, toward President Assad.

For those of you who know, who have been watching Syria, watching Assad, should this have been such a shocking move?