Christiane Amanpour is CNN's Chief International Correspondent. The opinions in this article belong to the author.

(CNN) For the first time in Syria's six-year civil war, the US has enforced its will , punishing what President Donald Trump said went "beyond a red line" for him.

As the British Defense Secretary Michael Fallon said on Sky News, Bashar al-Assad's use of chemical weapons presented the Trump administration with its first major test, and the US responded in an effort to deter further illegal use of WMD by the Assad regime.

And to many, the US strike refocuses on the real problem: Bashar al-Assad himself

The narrative about Syria has long been as confused as the endlessly morphing parties and proxies engaged in the war.

But that has always missed a key part of the picture, according to Assad's opponents: the strong-man president calls any opposition terrorism, and indeed shares responsibility for the rise of ISIS inside Syria by opening his jails when the war began in 2011 and unleashing violent Islamist prisoners to fight against the moderate opposition.

President Trump has gone through a 180-degree change on this issue. In 2013, he called on President Obama not to enforce his red line when Assad first used Sarin gas and killed more than 1,400 people near Damascus.

As candidate for president, Trump then accused Obama of not taking a tough enough stance in Syria, and even said the US should fight ISIS with Assad.

But after Tuesday's chemical attack in Idlib Province that killed more than 80 people, including 26 children, President Trump said that his "attitude toward Syria and Assad" had "changed very much."

Standing in the White House Rose Garden alongside the visiting King Abdullah of Jordan, a visibly shaken President Trump described the innocent men, women, and "innocent babies -- babies, little babies" who had died a slow and horrible death.

He said it was now his responsibility to respond to the chemical attack: "I will have that responsibility and carry it very proudly."

Afterwards, I spoke to Kassem Eid , an activist and former opposition fighter who survived that first Sarin attack in August 2013. He told me that President Trump's strong words made him feel "hope again."

"We've been left alone to suffer and get slaughtered and killed, while we were turned from humans into numbers, into statistics," he said.

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Days before Assad's chemical attack, the US had said it would only focus on ISIS, not on Assad.

"Our priority is no longer to sit and focus on getting Assad out," Ambassador to the UK Nikki Haley said last Friday, according to AFP.

Having dropped their mantra that "Assad must go," much of the international community is now admitting again that the main obstacle to peace in Syria is Bashar al-Assad and that there can be no future for Syria with him at the helm.

"We are trying to get the parties in Syria to agree on a situation in which President Assad plays no part," the UK's Fallon said.

"What happened in Idlib on Tuesday," Turkish Presidential Spokesman Ibrahim Kalin said, "proved again that the bloody Assad regime shows complete disregard for the prospect of a political transition and efforts to enforce the ceasefire."

The leaders of France and Germany released a joint statement urging a political transition.

The strike has been roundly praised by America's allies, even those who still worry and wonder what a Trump foreign policy will look like. And America's adversaries have been measured.

Russia, Assad's main military and political protector, of course condemned the strike, calling it an act of aggression and vowing to "bolster and increase the effectiveness of the Syrian armed forces' air defense systems."

But Russian Foreign Minister Sergey Lavrov also said that the damage to US-Russian relations would not lead to "an irreversible situation." And US Secretary of State Rex Tillerson will still visit President Putin next week in Moscow.

China, whose president was dining with President Trump in Florida at the very moment the strike was being carried out, has also been measured -- first condemning the use of chemical weapons, then expressing general opposition to the "use of force in international affairs."

The question is: What now?

Despite the rhetoric against Assad, Tillerson was quick to say US policy had not changed, and there is no indication of any military action to remove Assad from power.

ISIS remains the focus, and US-backed forces continue to encircle Raqqa, its base in Syria, ahead of an offensive designed to annihilate the terrorist group.

All we know for sure is that President Trump has taken one decisive step to prove that the United States will no longer tolerate the use of chemical weapons by the Syrian dictator.