Possible ramifications after an attack on Syria are among the concerns that Secretary of Defense Jim Mattis raised this week during national security meetings. It was still unclear if he had been satisfied with the continued planning, but he lowered the decision that Mr. Trump had initially promised on Monday that would come in 24 to 48 hours.
Mr. Mattis' caution, however, did not mean that Mr. Trump retracted an attack at some point. Given their Twitter messages promising to shoot missiles at Syria, government officials said they were in a situation that made it politically difficult, if not impossible, to withdraw.
A missile attack similar to the one Trump ordered last year would be criticized as inadequate. However, a more robust attack would increase the risk of a confrontation with Russia or Iran.
Sarah Huckabee Sanders, the White House press secretary, said all options remained on the table. She rejected the Russian denials that Syria was behind the alleged chemical attack during the weekend in the suburb of Douma in Damascus that the United States has blamed on the government of President Bashar al-Assad.
"We are confident again that Syria was responsible for this chemical weapons attack, but we also blame Russia for its failure to stop the chemical weapons attacks," he said.
The planning of a strike, in conjunction with France and Great Britain, progressed as the United States pressed its accusation against Syria for using gas to kill civilians during the long civil war.
At the United Nations, the US ambassador, Nikki R. Haley, accused Syria of using chemical weapons banned at least 50 times since the civil war started seven years ago, substantially higher than previous official estimates.
"Let's be clear: Assad's most recent use of poisonous gas against the people of Douma was not his first, second, third or even the 49th use of chemical weapons," Haley said. "The United States estimates that Assad has used chemical weapons in the Syrian war at least 50 times, and public estimates are as high as 200."
The accusation came during a scathing exchange between Ms. Haley and the Russian ambassador to the United Nations at a Friday meeting of the Security Council. Using chemical weapons is a war crime and the Syrian government is not the only actor in the war that has been accused of doing so.
"Our president has not yet made a decision about a possible action in Syria," Haley said. City Hall. "But if the United States and our allies decide to act in Syria, it will be in defense of a principle on which we all agree."
The Russian ambassador, Vasily A. Nebenzya, accused the United States and its allies of reckless warmongering. Mr. Nebenzya said there was no confirmed evidence that chemical weapons had been used in Douma and that the United States and its allies had "shown no interest in an investigation".
International chemical weapons inspectors were sent to Syria to conduct an investigation.
Mr. Trump's threats of a strike against Mr. Assad's forces, Mr. Nebenzya said, were "unworthy of a permanent member of the Security Council."
Mrs. Haley said she was incredulous at Mr. Nebenzya's defense of the Syrian government and his general portrayal of the events. "It surprises me how you say what you say with a serious face," he said.
For all that, Russia became big in the discussions in Washington on how to proceed. During a US military videoconference call, several officials expressed concern about the possible Russian reaction to an attack on Syrian installations, particularly in light of Moscow's threats to shoot down missiles.
During the call, military officials said it was imperative to take measures to protect American naval destroyers from Russian counterattacks. Donald Cook is in the Mediterranean and Porter is heading to the region. Both destroyers could take part in an attack launching Tomahawk cruise missiles.
But a possible online attack emerged as a possibility, and a way for Russia and Iran to avoid a direct confrontation with the United States military.
Just a few weeks ago, the Department of Homeland Security identified Russia as the source of malware "implants" in the US electrical network and released code samples to public services to help them clean up their systems. The warning accused Russia of mounting a series of intrusions against US and European nuclear power plants and water systems, in what analysts interpreted as a measure to test Moscow's capacity.
Iran hit US banks with a denial of service attack Six years ago, it tried unsuccessfully to manipulate a dam in Westchester County, New York. Iran is among the most sophisticated medium-sized powers in the use of cybernetic weapons, skills in which the country has invested heavily since the United States and Israel carried out an online attack on its nuclear enrichment sites.
While preparing the army for reprisals, Mattis has also warned of a possible counterattack of propaganda by Syria, Russia and Iran after a Western attack. Defense Department officials have stressed the need to show the world convincing evidence that the Assad government initiated a chemical attack on Douma.
Russian troops and mercenaries were deployed in Syria; Iranian forces and militias are also in the country and could retaliate against the thousands of US troops in Syria and Iraq. US personnel in Erbil, a Kurdish city in northern Iraq, for example, are preparing for a potential Iranian attack on their forces there, according to a US official.
Syria has already moved some of its planes to a Russian base in hopes of deterring Americans from attacking there and, in turn, igniting aggression between the two Cold War powers.
Senator Lindsey Graham, Republican of South Carolina, said he was concerned that military leaders were being too cautious. "I'm worried about whether or not we have the right generals with the right mindset," he said on Fox News Radio.
"If our military leaders are listening to Putin and we step back because Putin threatens to retaliate, that is a disaster for us all over the world," he added. "You can not let a dictator tell you what to do with another who has crossed two red lines."
Continue reading the main story