US Defense Secretary James Mattis was asked if the US and its allies planned to continue military operations beyond tonight's strikes in Syria.
He said it all depends on Syrian leader Bashar al-Assad.
"Should he decide to use more chemical weapons in the future and of course — the powers that have signed the chemical weapons prohibition have every reason to challenge Assad if should he choose to violate that, but right now this is a one-time shot and I believe that it sent a very strong message to dissuade him to, to deter him from doing this again."
What Trump said earlier tonight
However, earlier tonight, Trump indicated the strikes would continue until the Syrian regimes use of chemical weapons ends.
"We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents," Trump said.
Senate Minority Leader Chuck Schumer, who was reportedly on a commercial flight when President Trump announced the Syria strikes, has issued this statement warning the Trump administration to avoid getting the US in a "greater and more involved war in Syria."
Schumer, a New York Democrat, praised "the professionalism and skill of our Armed Forces" in April 2017, the last time Trump ordered strikes on Syria, saying it was "the right thing to do."
He also added that "it is incumbent on the Trump administration to come up with a strategy and consult with Congress before implementing it."
At least one US Navy warship based in the Red Sea participated in today’s strikes according to two US military officials.
US B-1 bombers were also used in the strikes in Syria, according to two US defense officials.
Anatoly Antonov, Russian ambassador to the US, issued a statement on Facebook in response to the strikes on Syria.
He accused the West of carrying out a "pre-designed scenario." He said there would be "consequences," and the responsibility for them lies with Washington, London and Paris.
Antonov added: "Insulting the President of Russia is unacceptable and inadmissible," and said that the US "has no moral right to blame other countries" since it possesses a large arsenal of chemical weapons of its own.
US Defense Secretary James Mattis was asked how the US could assure that the strike will work to stop the Assad regime from using chemical weapons again.
Mattis said "nothing is certain."
But this time, he said, the US used double the amount of weapons the military used in last year strike in Syria.
"It was done on targets that we believed were selected to hurt the chemical weapons program," he said. "We confined it to the chemical weapons type targets. We were not out to expand this, we were very precise and proportionate. But at the same time, it was a heavy strike.
What happened last year in Syria
One year ago the US launched its first military assault against the Syrian regime, a move some thought would be a game-changer in that country's gruesome civil war.
On President Trump's orders, US warships pummeled a government airbase with missiles on April 6, 2017, a day after more than 80 Syrians died in a chemical attack.
Trump said he took action in response because that chemical attack "crossed a lot of lines for me."
US Defense Secretary James Mattis told reporters that President Trump is legally authorized to order these Syria strikes — which were ordered without congressional authorization — under Article II of the Constitution.
It reads in part, "The president shall be Commander-in-Chief of the Army and Navy of the United States."
"We believe the president has ever reason to defend vital American interests and that is what he did here tonight under that authority," Mattis said.
Does that make this "legal"?
The Trump administration has suggested that they are, as an exercise of the President's inherent power under Article II of the US Constitution, according to CNN legal analyst and national security law professor Steve Vladeck the last time Trump ordered strikes on Syria.
At least judged against the constitutional text, historical practice, and contemporary understanding, this argument is a stretch -- but it's going to take a bit of work to explain why.
What does the Constitution say?
According to Vladeck, neither the text of the Constitution nor historical precedent conclusively settle when the president needs Congress to approve the use of military force. The Constitution divides the war powers between Congress and the President, and leaves unresolved exactly when uses of military force do and do not require Congress's sign-off.
Article I of the Constitution gives Congress the powers to "declare war," "raise and support armies," "provide and maintain a navy," and "make rules" to govern the military (and, perhaps most importantly, to fund all military operations), but Article II gives the President the "executive power," and makes him "commander in chief" of the military, powers that virtually all presidents have interpreted to give them at least some room to use the military without express permission from Congress.
Chairman of the Joint Chiefs, Gen. Joseph Dunford said the US "specifically identified” targets to “mitigate the risk of Russian forces being involved."
Gen. Dunford said the normal deconfliction line was used in the run-up to the strike to ensure clearance of airspace.
"We used the normal deconfliction channel to deconflict airspace. We did not coordinate targets,” Dunford said.
The missiles targeting Homs were intercepted and did not cause damage, according to a reporter on Syrian state TV in Homs.
General Joseph Dunford, chairman of the Joint Chiefs of Staff, told reporters tonight that this particular round of airstrikes are over.
"This wave of air strikes is over and that is why we're out here speaking to you now," he said.
However, defense officials made clear tonight in the Pentagon briefing that this is a sustained campaign, and strikes will officially end when the Syrian regime ceases its chemical weapons use.