WASHINGTON — President Trump made clear on Wednesday that missiles “will be coming” at Syria at any moment, telegraphing a military operation as he has previously said he would never do. But the real suspense remained — how many missiles, for how long, at what targets and to what end.
The strike that Mr. Trump was preparing as retaliation for a suspected chemical attack carries all sorts of perils that worry military planners and diplomats alike. A fresh intervention in one of the most combustible battlegrounds on the planet — one already crawling with Syrian, Russian, Iranian, American, Turkish and Kurdish forces — could easily bring unintended consequences.
The more expansive the strike, officials and experts said, the greater the risk of accidental casualties that could deepen the conflict with Russia or Iran. Yet a more restrained operation might not inflict enough damage on the government of President Bashar al-Assad to change his calculations.
If Mr. Trump goes beyond missiles and authorizes the use of manned aircraft even from outside Syrian airspace, they face the dangers of a modern air defense system provided by Moscow.
And Mr. Trump’s Twitter warning, along with the delay in acting, has given the Syrians as well as their Russian and Iranian allies days to prepare.
Two Defense Department officials said the Syrian military had moved some of its key aircraft to a Russian base, assuming the Americans would be reluctant to strike there. Russian commanders have also moved some of their military forces in anticipation of American action.
“You want to hit military targets, military equipment as much as possible, because it’s the Syrian military that’s carrying out these atrocities,” said Andrew J. Tabler, a Syria scholar at the Washington Institute for Near East Policy. “You want to make sure that you deliver a message and that you degrade their military capabilities.”