WASHINGTON—President Donald Trump is prodding his military advisers to agree to a more sweeping retaliatory strike in Syria than they consider prudent and is unhappy with the options they have presented to him, White House and other administration officials said.
In meetings with Secretary of Defense Jim Mattis, Mr. Trump has been pushing for an attack that not only would punish the Syrian regime but also exact a price from two of its international patrons, Russia and Iran, a White House official said.
“He wants Mattis to push the limits a little bit more,” the official said.
Mr. Mattis and other military advisers have resisted, worried that the administration lacks a broader strategy in Syria and that military strikes could trigger a dangerous clash with Russia and Iran, U.S. officials said.
Over the past two days, the Pentagon has had two opportunities to launch attacks against Syria in reprisal for a suspected chemical weapons attack, but Mr. Mattis halted them, according to U.S. and defense officials.
As a contingency, the military had identified potential windows for strikes, including one Thursday night, the U.S. and defense officials said. Mr. Mattis canceled them out of concerns that anything other than a “show strike” risked broader escalation with the Russians in particular, these defense officials said.
As a complex battleground filled with competing militias and foreign forces, Syria poses the toughest test yet of Mr. Trump as commander-in-chief. One year ago, he ordered a missile strike against an airfield in Syria in response to a chemical attack—a one-off event carried out by the U.S. alone.
This time, Mr. Trump is assembling an international coalition that presumably would take part in a military operation, a scenario that officials and experts have said requires careful choreography. He also faces a Pentagon leadership skeptical of the more muscular response he has advocated, according to White House and other administration officials.
Aides said Mr. Trump is tightly focused on the Syria problem and has been quizzing staff about the best response—even members of the legal team defending him in the Russia investigation. Mr. Trump has asked for briefing materials and was moved by images of children with foam bubbling from their mouths, symptoms of chemical weapons poisoning, aides said.
Still, the president has found time to tweet about a drama dominating the headlines: Former FBI Director James Comey’s new book. He labeled Mr. Comey an “untruthful slime ball” in a morning tweet.
At the president’s side as he weighs military action is John Bolton, a new national security adviser in his first week on the job.
Mr. Bolton favors a “ruinous” attack that would cripple some part of Syrian President Bashar al-Assad’s government and national infrastructure, according to a person familiar with his thinking. Mr. Bolton doesn’t want a reprise of the 2017 attack hitting an airfield that would be up and running in short order, this person said.
Mr. Trump’s national-security team was expected to meet again Friday afternoon to discuss the various approaches.
The debate over what to do in Syria marks the first time Mr. Mattis is making his case without support from former Secretary of State Rex Tillerson, who had aligned himself with the Pentagon chief on virtually every major security issue that came before the president.
This time, Mr. Mattis appears to be a lone voice of dissent in security meetings, U.S. officials said. Mr. Bolton, Acting Secretary of State John Sullivan, and U.N. Ambassador Nikki Haley all have expressed support for military strikes, U.S. officials said.
Mr. Trump’s eagerness to move quickly was evident at a cabinet meeting Monday when he said he expected the U.S. to make a decision that day on whether to hit Syria. Last year, the U.S. struck three days after a suspected Syrian chemical weapons attack; Friday marked the sixth day since the most recent incident, in Douma, Syria.
But the push for a quick strike was complicated by the challenges in confirming that Syria had used deadly gas in the attack and rallying support from key allies.
Damage Control
In anticipation of a U.S. strike, Syria and Russia in recent days have moved aircraft out of several air bases to other airfields.
50 miles
TURKEY
50 km
Afrin
Hasakah
Aleppo
Raqqa
Idlib
IRAQ
Khan
Sheikhoun
Deir Ezzour
SYRIA
Mediterranean
Sea
Homs
Areas of control
Palmyra
Russia/Iran/Syrian regime
LEBANON
Syrian Kurds
Opposition
Opposition/Turkey
Islamic State
Damascus
Douma
Site of suspected
chemical attack
Russian positions
Iranian positions
Syrian air bases
JORDAN
ISRAEL
Air bases Syria and Russia
have moved aircraft out of
50 miles
TURKEY
50 km
Afrin
Hasakah
Aleppo
Raqqa
Idlib
IRAQ
Khan
Sheikhoun
Deir Ezzour
SYRIA
Homs
Areas of control
Palmyra
Russia/Iran/Syrian regime
LEBANON
Syrian Kurds
Opposition
Damascus
Opposition/Turkey
Islamic State
Douma
Site of suspected
chemical attack
Russian positions
Iranian positions
Syrian air bases
JORDAN
Air bases Syria and Russia
have moved aircraft out of
50 miles
TURKEY
50 km
Afrin
Hasakah
Aleppo
Raqqa
Idlib
IRAQ
Khan
Sheikhoun
Deir Ezzour
SYRIA
Homs
Mediterranean
Sea
Areas of control
Palmyra
Russia/Iran/Syrian regime
LEBANON
Syrian Kurds
Opposition
Opposition/Turkey
Islamic State
Damascus
Douma
Site of suspected
chemical attack
Russian positions
Iranian positions
Syrian air bases
ISRAEL
JORDAN
Air bases Syria and Russia
have moved aircraft out of
Areas of control
Russia/Iran/Syrian regime
Syrian Kurds
Islamic State
Opposition/Turkey
Opposition
Russian positions
Iranian positions
Syrian air bases
Air bases Syria and Russia have moved
aircraft out of
50 miles
TURKEY
50 km
Afrin
Hasakah
Aleppo
Raqqa
Idlib
Deir Ezzour
SYRIA
Homs
Palmyra
LEB.
Damascus
Douma
IRAQ
Site of suspected
chemical
attack
JORDAN
Source: Institute for the Study of War. Control areas as of April 2.
“They want to make sure that Assad did it,” said former House Speaker Newt Gingrich, a Trump ally who talks frequently to the White House.
After last year’s strike, victims of the attack were transported to Turkey, where doctors were able to examine patients and conduct tests that showed the presence of a deadly nerve gas, sarin.
This time, the neighborhood hit by the gas attack is surrounded by Syrian regime forces, making it difficult for victims to get out or for independent inspectors to get in.
Russia said it conducted a quick investigation and determined that no gas was used. That raised suspicions that Russia and Syria had covered up any evidence, making it harder for independent investigators expected to arrive in Damascus to determine what really happened.
One U.S. official said the U.S. believed the Assad regime used barrel bombs to deliver the chemical attack on Douma, basing the assessment on U.S.-collected intelligence.
“We can say that the Syrian government was behind this attack,” said Heather Nauert, the State Department spokeswoman, referring to U.S. intelligence about the use of chemical weapons in Syria earlier this month. She said the U.S. government had “a very high level of confidence” in this assessment.
The debate within the administration was complicated by efforts to forge an international coalition. French President Emmanuel Macron was eager to take quick action after warning for months that he would strike Syria if Mr. Assad used chemical weapons, while British Prime Minister Theresa May has taken a more cautious approach.
Mr. Trump held several calls with Mr. Macron and Mrs. May, met with the emir of Qatar, and discussed Syria with Turkish President Recep Tayyip Erdogan.
The push for a quick response was also slowed by the need to move ships armed with cruise missiles into position near the Syrian coast. It took some time for the U.S., France and the U.K. to get ships into the eastern Mediterranean, where the U.S. Navy launched the Tomahawk missiles used in last year’s attack.
As the U.S. worked with its allies to craft a military response, Syria, Russia and Iran moved to protect their forces. Syria moved planes to Russian bases with better air defenses, U.S. officials said, making it harder to target them without hitting Russians.
On Wednesday, Mr. Trump again made clear his eagerness to strike on Twitter, warning Russia and Syria about an impending attack.
“Get ready Russia, because they will be coming, nice and new and ‘smart!’” he wrote. “You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!”
Mr. Trump derided his predecessor, former President Barack Obama, for issuing similar warnings to Syria in 2013. Mr. Trump’s public threat created unease among some U.S. officials as they watched Syria try to move its planes out of harm’s way.
On Thursday, as Mr. Macron said France had proof that Mr. Assad used chemical weapons in the attack, Mr. Trump sought to walk back his warning.
“Never said when an attack on Syria would take place,” he said in a tweet. “Could be very soon or not so soon at all!”
Russian officials have scaled back their rhetoric over a potential U.S. missile strike on Syria since Mr. Trump warned of the possibility of such an attack, limiting their comments to criticizing Washington of aggression.
None of the country’s top leadership, however, has contradicted Russian Chief of General Staff Valery Gerasimov’s threat last month to shoot down any missiles that could endanger Russian troops in Syria as well as to return fire.
Officials close to the Russian Defense Ministry have declined to say whether Russia would allow a strike to happen as long as it didn’t endanger Russian soldiers.
The United Nations Security Council held its fourth meeting this week on Syria, with Ambassador Nikki Haley telling diplomats: “Our president has not yet made a decision about possible action in Syria. But should the United States and our allies decide to act in Syria, it will be in defense of a principle on which we all agree.”
—Nancy A. Youssef and Michael C. Bender in Washington, Thomas Grove in Moscow and Farnaz Fassihi at the United Nations contributed to this article.
Write to Peter Nicholas at peter.nicholas@wsj.com, Gordon Lubold at Gordon.Lubold@wsj.com and Dion Nissenbaum at dion.nissenbaum@wsj.com
Appeared in the April 14, 2018, print edition as 'Pentagon Urges Caution on Syria Strike.'