A top Republican senator said the chemical weapons attack that killed dozens in Syria is a “defining moment” for President Trump to show his resolve in standing up against Damascus despot Bashar al-Assad.

“Well, it’s a defining moment in his presidency, because he has challenged Assad in the past not to use chemical weapons,” Sen. Lindsey Graham said on ABC’s “This Week.” “We had a one-and-done missile attack. So Assad is at it again. They see us, our resolve, breaking. They see our determination to stay in Syria waning. And it’s no accident they used chemical weapons.”

Trump, who in a tweet Sunday blamed Russia, Iran and former President Barack Obama for not stopping “Animal Assad,” suddenly announced last week that he intends to pull US troops out of Syria “very soon.”

“If it becomes a tweet without meaning, then he’s hurt himself with North Korea, and if he doesn’t follow through, he’s going to look weak in the eyes of Russia and Iran,” Graham said. “You need to follow through with that tweet. Show a resolve that Obama never did to get this right.”

Trump ordered a rocket attack on a Syrian airfield last April in retaliation for Assad’s use of chemical weapons against civilians.

His proclamation, made in a speech Thursday in West Virginia, caught many US military leaders off guard, prompting them to argue that the fight to drive Islamic State terrorists out of the war-torn country hasn’t finished yet.

The South Carolina lawmaker said withdrawing now would be an “utter disaster.”

“Have we learned nothing when what happens when you leave too soon? We pulled our troops out of Iraq. ISIS came back,” he said.

GOP Sen. Susan Collins of Maine said the chemical attack on civilians in Douma, a rebel-held area in the Damascus suburbs, should make the president reconsider his vow to remove troops from the country.

“I think the president is going to have to reconsider his plan for an early withdrawal in light of what has happened,” she said on CNN’s “State of the Union.”

She said the attack also gives Trump reason to put pressure on Moscow.

“Last time this happened, the president did a targeted attack to take out some of the facilities that may be an option that we should consider now, but it is further reason why it is so important that the president ramp up the pressure and the sanctions on the Russian government because, without the support of Russia, I do not believe that Assad would still be in office,” Collins said.

White House homeland security adviser Tom Bossert called the chemical attack an “unacceptable practice” and said Trump could punish Syria.

“I wouldn’t take anything off the table. These are horrible photos, we’re looking into the attack at this point, ” he said on ABC’s “This Week.”

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But he also said the international community is going to have to step in to help the United States police dangerous places like Syria.

“American troops aren’t going to fix the six or seven different ongoing conflicts and wars going on in the Middle East or in Syria at this stage,” he said. “We need regional partnership increased and we need US presence decreased.”