No doubt fearing the grave risk of killing Russian military personnel on the ground in Syria, the United States military gave Russia advance notice before launching cruise missile strikes overnight on a Syrian air base that is used to store chemical weapons, according to a U.S. intelligence assessment.

A Pentagon spokesman, Capt. Jeff Davis, said in a statement that a pre-exiting “deconfliction” channel, set up to keep American and Russian jets from crossing paths in the skies over Syria, was used to disclose the planned attack to Russia. “U.S. military planners took precautions to minimize risk to Russian or Syrian personnel located at the airfield,” Davis said.

(After the strikes hit, the Russians announced that they were withdrawing from the agreement to share information about their movements over Syria.)

According to Davis, the strikes were aimed not at Syrian soldiers but the “aircraft and support infrastructure and equipment at Shayrat Airfield,” with the intention of “reducing the Syrian Government’s ability to deliver chemical weapons.” In his statement announcing the strikes on the airfield, President Donald Trump said that the base in central Syria had been used on Tuesday to launch a chemical attack that killed dozens of men, women and children in the rebel-held town of Khan Sheikhoun in Idlib Province.

Evidence of the damage caused by the strikes is incomplete, but images of the base broadcast on Russian state television on Friday suggested that significant parts of it remain intact.

Evgeny Poddubnyy, a Russian war correspondent, posted more images of the damaged airfield on Instagram, showing a bunker reduced to rubble and what might have been a jet, but another plane that looked unscathed.

Video posted on YouTube by a news site in St. Petersburg, Federal News Agency, also appeared to show an air defense battery at the perimeter of the base had escaped the bombing.

It is not yet clear how far ahead of time the Russians were warned, but a witness told Riam Dalati of the BBC that a convoy of Russian military vehicles left the base at some stage yesterday.

Although at least six Syrian airmen died in the attack, according to a Syrian military spokesman, it seems inconceivable that the Russian military personnel fleeing the base would not have alerted their allies to what was coming.

Video recorded by a Russian military drone over the base suggested to some observers that the Syrians might have moved some of their jets out of their bunkers in anticipation of the strikes.

While it was no doubt prudent to take steps to minimize the number of people killed in the attack, letting Syria know that the strike was coming represents a significant departure from Trump’s own campaign rhetoric. At rally after rally before he was president, and in debates against Hillary Clinton, Trump repeatedly called for surprise attacks and mocked the U.S. military and its Iraqi allies for giving advance notice of a planned offensive against Islamic State fighters to retake the city of Mosul in Iraq.

“Whatever happened to the element of surprise?” Trump asked in a September debate. “Douglas MacArthur, George Patton, spinning in their graves when they see the stupidity of our country.”

“Why don’t we just go in quietly, right?” Mr. Trump told supporters in Wisconsin at one campaign rally in late October. “They used to call it a sneak attack.”

Pressed on the idea that he did not understand military strategy in an interview just before the election, Trump vowed to teach military experts a thing or two.

In a video statement on the impact of Trump’s non-surprise attack in the Syrian air base, a Russian military spokesman mocked it as ineffective, saying that just six MIG-23 jets were destroyed, while the runways and bulk of the Syrian jets were unharmed.

A screenshot from a video statement released by Russia’s defense ministry on Friday.

The Russian spokesman also scoffed at the notion that Syria’s government was responsible for the chemical attack this week — reiterating his government’s claim that Islamist rebels were producing their own nerve agents — and suggested that Trump had staged the incident purely for reasons of domestic politics.

Setting aside their feelings about Trump, Syrian activists who want to see President Bashar al-Assad forced from power largely welcomed the strikes.

Some, however, expressed their dismay that Trump’s message seemed to imply that Assad would be punished only for killing civilians with chemical weapons.

The strikes were also welcomed in rebel-held northern Syria, according to Quentin Sommerville of the BBC and Clarissa Ward of CNN.

One Syrian blogger, who writes under the pen name Edward Dark, noted bitterly that Trump’s strikes had thrilled the Islamic extremists he has vowed to defeat, while potentially exacerbating the refugee crisis whose victims he has treated with such disdain.