Bodies of victims of an alleged chemical attack lie on the ground in rebel-held Douma, Syria. (Emad Aldin/EPA-EFE/REX/Shutterstock)

Last weekend, at least 40 Syrians were killed in an apparent chemical attack.

The United States has blamed the government of Syrian President Bashar al-Assad. And President Trump has promised a"very, very tough” response, and soon. “Everybody's going to pay a price,” he told reporters Monday. “If it’s Russia, if it’s Syria, if it’s Iran, if it’s all of them together, we’ll figure it out, and we’ll know the answers quite soon.” On Wednesday, he tweeted that missiles “will be coming” toward Syria and taunted Russia for vowing to shoot them down.

What's less clear is what shape a U.S. response might take. Last year, Trump reacted to a large-scale chemical attack with a targeted airstrike. The military fired 59 Tomahawk cruise missiles at a Syrian air base, damaging about 20 Syrian aircraft.

Experts suggest that Trump may authorize a similar attack this time, targeting one or several air bases. Officials say the president is also considering targeting supply flights sent by Iran and economic sanctions against Russia and Syria. “The likeliest option is exactly what we saw before — an airstrike that the president puts forward as a so-called tough response but doesn't do very much to degrade Assad’s forces or to punish him for his ongoing use of chemical weapons,” Jonah Blank, an analyst at the Rand Corp., told USA Today.

Is there anything the United States could do that might dissuade Assad's forces from gassing their people? We put the question to experts.

As a line of deterrence, last year's strike was “not nearly as permanent as we would have hoped,” Melissa Dalton, of the Center for Strategic and International Studies, told me. But it's challenging to imagine how the United States might scale up without triggering a similar kind of escalation from Russia and Iran.

Her recommendation: Mobilize a coalition to respond, one that includes Washington's European allies along with Arab partners in the Persian Gulf. And pair any military approach with a much stronger effort to investigative the Assad regime — to try to understand what's happened and what kind of chemical weapons the Syrian government still has in stock. That effort should also involve getting rid of chemical weapon stockpiles.

In theory, this is a job for the United Nations. But it has been hard for the international body to fulfill that role, since Russia and China sit on the Security Council and can veto any push for broader action. One possibility is a French proposal to build up a “parallel investigative structure,” Dalton said.

“Something that could get to the bottom of things, collecting evidence and getting it to channels for seeking accountability,” she said.

The  Trump administration might also consider whether it wants to hold fast to its earlier announcement that all U.S. troops will be out of Syria in the next six months. Dalton said she thinks that announcement may have emboldened Assad and his allies to act.

There is evidence, too, that a targeted military strike may not have much of an impact. Dalton said she has heard reports that Russians are jamming drone flights by the United States and its allies, and that the Assad regime is moving its personnel and assets around in anticipation of U.S. action.

“I worry that the administration is going to focus on the immediate military options available,” she said. Even if it engages a coalition, something Dalton sees as a positive step, she wonders whether there will be enough linkage to holistic efforts to leverage any real change.

Michael Rubin, a former Pentagon official under President George W. Bush, has a bolder proposal: targeting Assad. “If [Trump] is serious about restoring a deterrent to the use of chemical weapons, then he should not rely on some symbolic cruise missile response,” he wrote in a Washington Examiner opinion piece.

An airstrike against Assad might target his palace in Damascus, or even Assad himself. “While Russia warns the United States not to retaliate in Syria, permanently removing Assad from the battle field would leave Moscow no choice but to begin serious negotiations on who comes next. Simultaneously, the Kremlin would think twice about allowing its other clients in the future to stray so far from the rules of war,” he wrote.

An attack on a military base, Rubin argued, would hit Syrian conscripts rather than the country's leadership. Rubin likened Trump's options in Syria to trying to figure out what to do with a hornet's nest.

“With a hornet's nest, you have two good options,” he said. “One, leave it alone. Two, get rid of it. Taking the middle ground and tapping it with a stick is the worst of all possible options.”