WASHINGTON — President Donald Trump said Wednesday the suspected chemical bomb that killed dozens in Syria “crossed a lot of lines” for him and has altered his view of the country’s leader, Bashar al-Assad.

Trump would not say how the United States will respond or whether it will use military might, but he signaled a potential pivot from remarks last week by top aides who said he would not prioritize ousting Assad to end the civil war.

Trump sharpened his criticism of the Syrian government as he lamented the civilian casualties — “even beautiful little babies” — in rebel-held Idlib as “an affront to humanity.”

Speaking at a White House Rose Garden news conference with visiting King Abdullah II of Jordan, Trump appeared to have been moved by the images of children who lay lifeless or struggling to breathe in the wake of an apparent nerve gas attack from a government airstrike.

“That attack on children yesterday had a big impact on me,” he said. “ . . . And I will tell you it’s already happened that my attitude toward Syria and Assad has changed very much.”

Some of the graphic photographs that have gripped the world were held up by U.S. Ambassador to the United Nations Nikki Haley during an emergency UN session, where she suggested the United States could resort to unilateral action against Syria if the UN doesn’t condemn the attack.

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A day earlier, Trump had addressed the violence only through his press secretary and in a written statement, which pinned blame on his predecessor’s “weakness and irresolution.”

Trump’s criticism came despite tweeting repeatedly in 2013 and 2014 that Obama should stay out of Syria.

On Wednesday, he again faulted former President Barack Obama for failing to seize a “great opportunity to solve this crisis a long time ago” and making a “blank threat” when he warned Assad of a red line then watched him cross it.

But Trump also accepted that the Syrian civil war is now on his shoulders. “I will have that responsibility and carry it very proudly,” he said. “It is now my responsibility.”

Trump did not speak about Russian Federation leader Vladimir Putin’s alliance with Assad, but Haley addressed it at the United Nations, placing Russia in the context of other despotic governments.

“The truth is that Assad, Russia and Iran have no interest in peace,” she said, adding, “How many more children have to die before Russia cares?”

She suggested a readiness for a solitary U.S. response.

“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,” she said.

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Some Democrats on Capitol Hill have called the Syrian chemical bombing a war crime.

Senate Minority Leader Chuck Schumer at a Wednesday news conference said Trump placed culpability on Obama, but hasn’t made clear his own next steps in response to Assad.

“Instead of action, there’s just blame,” Schumer (D-N.Y.) said. “Blame doesn’t solve the problem.”

At the Rose Garden news conference, Trump commended King Abdullah for hosting Syrian war refugees in his country.

Trump said the United States has contributed additional humanitarian assistance to Jordan to help the effort.

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The king was asked about the Trump administration’s efforts to restrict the entry into the United States of citizens of Muslim-majority countries, including Syria, as well as refugees.

“I think, as the president pointed out, most, if not all, Syrian refugees actually want to go back to Syria,” he said.

With Zachary R. Dowdy