President Donald Trump said in a joint news conference with Jordanian King Abdullah II bin Al-Hussein Wednesday his approach to Syria and Syrian president Bashar al-Assad is changing, especially in the wake of the “unacceptable” suspected chemical attacks that killed dozens Tuesday.

“That attack on children had a big impact on me,” Mr. Trump said. “Big impact.”

Mr. Trump’s response to questions about the chemical attack in Syria that killed at least 72 people didn’t rule out the possibility of military intervention in Syria, a seeming switch from the administration’s past reluctance to intervene in Syria and the Assad regime. Mr. Trump said the apparent chemical attack Tuesday, following previous similar attacks, “crossed a lot of lines for me,” and that his attitude towards Syria and Assad has already changed — “very much.”

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“That was a horrible, horrible thing,” Mr. Trump said. “And I’ve been watching it and seeing it, and it doesn’t get any worse than that. And I have that flexibility. And it’s very very possible, and I will tell you, it’s already happened, that my attitude towards Syria and Assad have changed very much.”

Mr. Trump said the gas attacks take the conflict in Syria to a “whole different level,” and although he would have preferred to never enter the Middle East, ISIS formed in a vacuum after the U.S. began to withdraw. But the president, pressed further about whether his reluctance about getting involved in Syria has changed, said, as he customarily does, that he prefers not to elaborate on any military plans, as previous administrations have done.

“I’m not saying I’m doing anything one way or the other,” Mr. Trump said.

The president didn’t bring up Russia, which has said former president Barack Obama’s “red line” remarks prompted the attacks. Obama dubbed the use of chemical weapons in Syria as a “red line,” an ultimatum that led to threats of physical force against Assad before a peaceful resolution was reached instead.

Another issue that did not come up at Wednesday’s press conference was the White House memo that no longer lists chief strategist Steve Bannon on the National Security Council’s Principals Committee. That group consists of the president’s top national security officials and considers how policy affects national security.

Abdullah also condemned the chemical attack in Syria, saying it was a result of international failures. Assad said he “fully” supports and endorses the president as he looks at the possibility of intervening abroad.

Abdullah expressed his appreciation and support of Mr. Trump in the fight against terrorism.

“Terrorism has no borders, no nationality, no religion,” Abdullah said, adding the role of the U.S. is “key.”

Abdullah said the U.S. can’t do all of the heavy-lifting,” emphasizing the need of foreign countries to aid the U.S. to eliminate this “national scourge” of terrorism.

Abdullah is often considered one of the closest, if not the closest, U.S. allies in the Middle East. This isn’t the first time Mr. Trump has met with the Jordanian king. Mr. Trump in February met with Abdullah and discussed the possibility of establishing safe zones in Syria.

1:36 p.m. The press conference has ended.

1:27: Mr. Trump said the chemical attack in Syria has had a “big impact” on him — so much so that he is approach to Syria and Assad “has changed very much.”

“That attack on children had a big impact on me,” Mr. Trump said. “Big impact.”

1:24: Mr. Trump, asked if he still blames former President Obama for the Syrian chemical attacks, said he thinks the Obama administration missed a great opportunity. But pressed further, he said he bears the responsibility for what happens abroad going forward.

“I now have responsibility and I will have that responsibility and carry it very proudly,” he said.

1:22 p.m. Abdullah says the Syrian chemical attack is a result of international failures, and said he “fully” supports and endorses the president as he looks to intervene abroad in Syria.

1:18 p.m. Abdullah says he and Mr. Trump have had a “very good round of talks,” and thanks Mr. Trump for his partnership, particularly in the fight against terrorism.

“Terrorism has no borders, no nationality, no religion,” Abdullah said, adding the role of the U.S. is “key.” But Abdullah said the U.S. can’t do all of the heavy-lifting,” emphasizing the need of foreign countries to aid the U.S. to eliminate this “national scourge” of terrorism.

1:15 p.m. Mr. Trump says the fight against ISIS will be “shorter” than many people think it will be.

1:14 p.m.: Mr. Trump says Jordan has tremendous support from the U.S., thanks Abdullah for his partnership. Mr. Trump says the U.S. is “blessed” to have such a determined partner in Abdullah.

1:12 p.m.: Mr. Trump opens with the Syrian chemical attack horrific, decries horror of the deaths of even “beautiful little babies.” Mr. Trump says these horrors of the Assad “regime” “cannot be tolerated.”

1:11 p.m. Mr. Trump and King Abdullah II enter the White House Rose Garden.