Clearly emotional, Trump said a chemical attack in Syria that killed scores of civilians, including children, "crossed a lot of lines for me."
"When you kill innocent children, innocent babies - babies! - little babies," Trump said, "that crosses many, many lines. Beyond a red line, many, many lines."
Trump said the multifaceted conflict "is now my responsibility," and he appeared to reckon with the same lack of good options in Syria that repeatedly confounded former president Barack Obama.
Like Obama, Trump faces a Syrian strongman willing to commit atrocities and whose military and diplomatic backing from Russia has prolonged a civil war with numerous belligerents, separate from the campaign to defeat the Islamic State.
Trump suggested that the attack Tuesday had changed his mind about his approach to Syria, which had seemed to focus exclusively on defeating the Islamic State, but he did not say what that might mean.
"I like to think of myself as a very flexible person," Trump said in a Rose Garden news conference with visiting Jordanian King Abdullah II.
"And I will tell you that attack on children yesterday had a big impact on me, big impact. That was a horrible, horrible thing," Trump said. "I've been watching it and seeing it, and it doesn't get any worse than that."
The president would not say whether military action against the government of Syrian President Bashar Assad is more likely as a result of the attack, and he did not address whether his concern on behalf of the dead and injured civilians had changed his mind about the wisdom of accepting Syrian refugees into the United States.
But he did say his "attitude toward Syria and Assad has changed very much."
U.N. Ambassador Nikki Haley suggested the United States could intervene militarily, although she, too, was not specific about what that might entail.
"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," Haley said. "For the sake of the victims, I hope the rest of the council is finally willing to do the same."
If proven to have been carried out by Assad, the chemical attack Tuesday would represent a challenge to Trump to act where Obama did not. The attack followed recent Trump administration statements backing away from Obama's insistence that Assad must leave power as a part of any political settlement in Syria.
Trump did not call for Assad to go and said nothing about Russian culpability for backing the regime and defending it against charges that it targeted civilians. The Assad government and Russia blamed the chemical release on rebel forces.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said that at least 72 people were killed, making it the deadliest chemical assault since 2013, when the Syrian government dropped sarin on the Damascus suburbs, killing hundreds of people as they slept, and bringing the United States and European allies to the verge of military intervention.
On Wednesday, Trump repeated campaign-trail criticism of the Obama administration for threatening military action over that 2013 attack and then backing off. For the balance of his presidency, Obama struggled with the limits of an arm's-length approach that he maintained was still preferable to direct military involvement.
"We have a big problem. We have somebody that is not doing the right thing. And that's going to be my responsibility," Trump said. "But I'll tell you, that responsibility could've made, been made, a lot easier if it was handled years ago."
Trump had supported Obama's decision not to bomb in 2013, but as a candidate, he used the episode as an example of what he called the Democrat's weakness and indecision. Trump promised certitude and strength, and there were echoes of that rhetoric in his first Rose Garden news conference Wednesday.
"We will destroy ISIS and we will protect civilization," Trump said, referring to the Islamic State group that operates in Syria and Iraq and is one of many players in the fractured country. "We have no choice. We will protect civilization."
Abdullah, whose small country has been overwhelmed by Syrian refugees, largely dodged a question about whether Trump's proposed travel ban, which would block Syrians from coming to the United States as refugees, would add to Jordan's burden.
In the past, attacks on civilians such as the one Tuesday have increased the pressure on Syrians to flee.
Earlier Wednesday, Haley assailed Russia in blunt terms for protecting the Syrian government, saying that Moscow is callously ignoring civilian deaths.
"How many more children have to die before Russia cares?" she said in New York, with representatives of the Syrian government and its Russian backers looking on.
She held aloft gruesome images from the attack in Idlib province. One showed a child splayed and apparently lifeless.
"Russia has shielded Assad from U.N. sanctions. If Russia has the influence in Syria that it claims to have, we need to see them use it," Haley said. "We need to see them put an end to these horrific acts."
At the United Nations, Russia's representative lamented what he called "clearly an ideological thrust" to the discussion at the Security Council.
Accusations of the Assad regime's involvement are "closely interwoven with the anti-Damascus campaign, which hasn't yet reached the place it deserves on the landfill of history," Russian representative Sergey Kononuchenko said.
Russia is likely to block a proposed Security Council condemnation of the attack.
Syria's representative, Mounzer Mounzer, dismissed the accusation that his country is to blame, saying Damascus condemns the use of chemical weapons. "We don't have them. We never use them," he told the council.
Under Russian pressure, Syria agreed in 2013 to give up its chemical weapons and claimed it had eliminated its stockpiles.
Russia tried Wednesday to shift the blame to armed groups opposing Assad.
Maj. Gen. Igor Konashenkov, a Russian military spokesman, said Syrian warplanes had been targeting rebel workshops and depots.
"The territory of this storage facility housed workshops to produce projectiles filled with toxic agents," he said in a recorded statement.
The World Health Organization said Wednesday that victims' symptoms bore all the hallmarks of a chemical attack, possibly involving a banned nerve agent. Syrian forces also have used chlorine-based weapons.
The U.N. ambassadors to Britain and France criticized Russia directly for protecting the Assad government at the expense of civilians.
"History will judge all of us in how we respond to these unforgettable and unforgivable images of the innocent," British Ambassador Matthew Rycroft said. "How long are we going to sit here and pretend that actions in these chambers have no consequences?"
He said Russia and China squandered an opportunity to call out Syria when they vetoed a February effort to condemn smaller reported incidences of chemical weapons use.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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