WASHINGTON — President Donald Trump’s “America first” doctrine holds true in the wake of the U.S. missile strike in retaliation for the deadly chemical attack on Syrian civilians, White House spokesman Sean Spicer said Monday.

“Our national security is the first and foremost reason that we have to act,” the press secretary said, adding that the spread of chemical weapons is a “clear danger to our country.”

Trump is prepared to take further military action against Syrian President Bashar Assad’s government for its use of poison gas as well as more conventional barrel bombing, Spicer said.

Trump received plaudits after his decision Thursday to hit a Syrian airfield with nearly 60 cruise missiles. He said he was moved by the graphic images of babies either dead or struggling to breathe after an apparent poison gas attack by Assad’s forces.

Secretary of Defense Jim Mattis said in a statement Monday that the U.S. missiles had taken out “20 percent of Syria’s operational aircraft” and also damaged or destroyed the country’s fuel and ammunition sites and air-defense capabilities.

“The Syrian government would be ill-advised ever again to use chemical weapons,” Mattis warned.

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Spicer went further by condemning conventional tactics.

“When you watch babies and children being gassed and suffer under barrel bombs, you are instantaneously moved to action,” he told reporters.

He was asked about Trump’s foreign policy stance in the context of tweets the president sent as a private citizen urging then-President Barack Obama to stay out of Syria and remarks Trump made as a candidate saying he won’t be “president of the world” and Americans won’t be “policemen of the world.”

Spicer responded, “We have to have a clear and defined national interest wherever we act.”

The press secretary also appeared to distance the administration from Russia, saying it’s part of a small group that is “not with us,” including Syria, Iran and North Korea.

Secretary of State Rex Tillerson is set Tuesday to begin meetings in Moscow, marking the first visit to Russia by a Trump administration official. He has said he would pressure Russia for failing to fulfill its commitment to dismantling Syria’s stockpile of chemical weapons.

Tillerson and U.S. Ambassador to the United Nations Nikki Haley on Sunday TV talk shows presented somewhat different priorities when it comes to Trump’s next steps abroad.

Tillerson said the United States’ first priority is defeating the Islamic State while Haley said targeting the Islamic State and ousting Assad are among “multiple priorities.”

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Spicer tried to bridge the statements.

“I think, right now, the focus is twofold. One is defeating ISIS and the second is creating the political environment necessary for the Syrian people to have new leadership,” he said while noting later, “Our No. 1 priority is to defeat ISIS.”

Spicer said he believes the Islamic State can be defeated with Assad still in power.

He also characterized as “overblown” the reported West Wing tensions that put chief strategist Steve Bannon and Trump senior adviser and son-in-law Jared Kushner at odds.

Trump wanted a “diverse set of opinions” among his top aides, Spicer said.

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The Associated Press had reported that Trump’s team is going back to the drawing board on its blueprint to overhaul the tax code and won’t make its August target date.

Spicer called the report inaccurate and said the administration is going through the process of drafting a tax-reform plan by meeting with groups and lawmakers.

“This is going to be a major undertaking,” he said.