The Trump administration must back up its tough talk with real action against Bashar al-Assad’s regime in Syria, including by destroying the Syrian government’s ability to use chemical weapons against its own people, according to the lead negotiator for the Syrian opposition.

Riyad Hijab, the head of the High Negotiations Committee that represents the Syrian opposition in the international political process, happened to be in Washington this week when the Syrian government perpetrated its latest chemical weapons attack, killing dozens of innocent men, women and children in Idlib province. Assad’s flagrant use of banned weapons to murder civilians is a direct challenge to Trump, the former Syrian prime minister told me in an interview. Trump said the right things, but nobody knows whether he will back up those words with action.

“We expect deeds from President Trump, not words,” Hijab said. “We want deeds to protect the Syrian civilians and to protect the entire region, and to protect the American people as well. This is a defiance to President Trump in front of the American people and the entire world.”

The Syrian opposition is calling on the Trump administration to take military action to destroy Assad’s chemical weapons stockpiles as well as its means of delivering those weapons. That would include destroying the runways and airplanes Assad uses to bomb civilian areas as well as the missile launchers that have been used to drop chemical weapons on civilians in the past.

“These weapons must be destroyed,” Hijab said. “The airplanes and the runways must be destroyed. All the weapons that are killing the Syrian people must be destroyed.”

Key moments from President Trump's joint news conference with King Abdullah II of Jordan (Sarah Parnass/The Washington Post)

An outraged Trump on Wednesday condemned Assad for using chemical weapons and pledged to take action in response. “It is now my responsibility,” Trump said while standing alongside Jordan’s King Abdullah II at the White House. “My attitude toward Syria and Assad has changed very much. … It crossed a lot of lines for me.”

Nikki Haley, the U.S. ambassador to the United Nations, told the U.N. Security Council that if the world does not act collectively in response, the United States may “take our own action,” although she declined to specify what that might be.

Hijab said the Trump administration must find a way to get past the Russian roadblock at the Security Council to compel collective action by that body. Also, the United States should reinvest in supporting a political process that can lead to a transitional government and Assad’s departure.

There is a role for Russia in solving the Syrian crisis, according to the opposition. Russia shares the opposition’s desire to keep the Syrian state intact, preserve its institutions and protect its minorities. But Russia, which has launched thousands of airstrikes against the Syrian opposition, must be persuaded or pressured to break with Assad.

“You cannot eliminate terrorism if Assad remains in power, and you cannot eliminate Iranian influence if Assad is in power,” said Hijab.

The last time the United States threatened strikes against the Assad regime, after the killing of more than 1,400 civilians with chemical weapons in 2013, one of the loudest and most consistent opponents of that action was Trump. He and other critics of that idea argued that the United States would only find itself entangled in another Middle East conflict that doesn’t impact core U.S. interests and risks sparking a dangerous military escalation with Russia.

Those arguments are exactly what prevented President Barack Obama from acting in 2013, and since then, the situation has only gotten worse, said Hijab. Hijab shares Trump’s criticism of Obama’s Syria policy, which he sees as a moral and strategic failure of historic proportions.

“The Obama administration is the one that led to this tragic situation,” he said. “I don’t think history will forgive Obama for what he’s done in Syria. How can Obama look at the faces of these children now and at the same time look at his children?”

The Syrian opposition is also asking the United States to support a new effort to train and equip moderate rebel fighters to combat the Islamic State, especially in the eastern regions of Deir al-Zour and Raqqa. Several previous attempts to build up a rebel force have failed and U.S. support to Syrian rebels has essentially ceased, Hijab said. But despite past failings, there is still a dire need to support Sunni Arab fighters to take and hold Sunni Arab lands and prevent them from falling into the hands of the extremists.

“The only solution is to build a partnership between you and us in order to together fight against al-Qaeda and ISIS,” Hijab said.