In the wake of last weekend's gruesome attack, some US officials advocated a larger, and therefore riskier, strike than the limited action Trump ordered in April 2017, also in response to suspected chemical weapons use.
In his televised address from the White House on Friday evening, Mr Trump said the U.S. was prepared to sustain economic, diplomatic and military pressure on Mr Assad until the Syrian leader ends what the USA president called a criminal pattern of killing his own people with internationally banned chemical weapons.
One of the officials noted that Syria and Russian Federation relocated their equipment and personnel a year ago - the first and only other time Mr Trump ordered missile strikes on Syria in response to a chemical weapons attack.
"Get ready, Russia, because they will be coming, nice and new and "smart".
In one his tweets on Wednesday, Mr Trump called the Syrian leader a "gas killing animal".
"The US has to be very careful not to accidentally strike Russian targets or kill Russian advisors", Ben Connable, a senior political scientist at the RAND Corporation, told AFP.
Later in the day, after Trump had met with his national security team, White House Press Secretary Sarah Sanders said, "we are continuing to assess intelligence and are engaged in conversations with our partners and allies".
Saturday's suspected poison gas attack took place in a rebel-held town near Damascus amid a resumed offensive by Syrian government forces after the collapse of a truce.
Under no circumstances should President Donald Trump authorize action against Syrians that could lead to wider military involvement there.
"In any event, the United States, under my Administration, has done a great job of ridding the region of ISIS", the President wrote in the same tweet.
In London, British Prime Minister Theresa May held an emergency cabinet meeting to discuss support for USA action against the Syrian regime.
What if Russian Federation does shoot down USA missiles?
Gen. Joseph F. Dunford Jr., chairman of the Joint Chiefs of Staff, said the only communications that took place between the United States and Russian Federation before the operation were "the normal deconfliction of the airspace, the procedures that are in place for all of our operations in Syria".
Haley said the three USA goals for accomplishing its mission are making sure chemical weapons are not used in a way that could harm US national interests, defeating the Islamic State group and having a good vantage point to watch what Iran is doing.
Targeted economic sanctions against Syria and its allies, Iran and Russian Federation could still be used. Trump said on Twitter. Vladimir Shamanov, who chairs the defense committee of the lower house, said the vessels had departed the base for their own safety, which was "normal practice" when there were threats of attack.
On Thursday, US officials said they had blood and urine samples from victims which had tested positive for chlorine and a nerve agent, according to a NBC News report.
Mattis, however, said the assault was a "one-time shot", so long as Assad does not repeat his use of chemical weapons.
White House officials did not reply to a request for more detail on Trump's remarks.
On Wednesday, a top official from Iran, Assad's other main ally, toured eastern Ghouta and vowed to stand by Syria in the face of "any foreign aggression". Are these purely punitive strikes, taken to make the worldwide community feel better about retaliating for the brutal death of children (leaving aside those killed over the last seven years by bombs and guns, as well as other unanswered chemical weapons attacks)? The Syrian government and Russian Federation have called reports of the attack bogus.
The strike could also target what is left of Assad's air force and air defenses, though the delay between Saturday's attack and an eventual retaliatory strike means he likely will have moved his warplanes to safety.
Pushkov added that the USA can not reverse or change the conflict in Syria without sending several tens of thousands of its soldiers there. USA allies, including France and Great Britain, are also considering responses.