Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of " United States of Jihad: Investigating America's Homegrown Terrorists ."

(CNN) Asked what would shape the future of his government, British Prime Minister Harold Macmillan is said to have remarked "Events, dear boy, events."

The Trump administration just had its first big international event: Syrian dictator Bashar al-Assad's regime appears to have carried out a chemical attack against its own people, killing dozens, including many women and children.

The video images of young children writhing in agony and being hosed down with water are indelible. And those images certainly now have the attention of President Donald Trump, who said on Wednesday , "I will tell you, what happened yesterday is unacceptable to me ... It's already happened that my attitude toward Syria and Assad has changed very much."

So what can be done? When you are President and an international crisis lands in your inbox, there are generally no easy options, just a menu of unappetizing least-bad options to choose from. Already Trump and his national security team are considering some kind of military option. But they may have to move forward without either a UN resolution or congressional authorization -- and whatever action the United States takes will suck it further into the morass of the Syrian civil war and even possibly into some kind of confrontation with the Russians, Assad's staunchest backers.

On the campaign trail, candidate Trump occasionally raised the idea of creating "safe zones" for Syrian civilians. He never elaborated on where those zones would be, nor did he say how they would be enforced.

Neither has his Secretary of State, Rex Tillerson, who hosted a conference in Washington of the coalition of 68 anti-ISIS countries. The event was notable for the lack of news that came out of it, except for one brief comment that Tillerson made about creating "interim zones of stability, through ceasefires, to allow refugees to return home." Tillerson didn't explain how these zones of stability would work.

The United Nations is considering a resolution that would condemn the Assad regime for the suspected nerve gas attack . These kinds of resolutions have always failed in the past because Russia invariably backs Assad and will almost certainly veto it -- as will China.

For obvious reasons, neither Russia nor China are in favor of UN resolutions that condemn the human rights abuses of authoritarian regimes and that may even lead to their ouster. Both China and Russia felt duped by the UN "no-fly" zone resolution regarding Libya in 2011 that eventually led to the ouster of Libyan dictator Moammar Gadhafi. China and Russia had abstained from the Libyan resolution and neither country plans to make what they regard as a similar mistake again.

In the absence of some kind UN resolution on Syria, could the United States take unilateral action? US Ambassador to the UN Nikki Haley acknowledged the possibility on Wednesday. "When the United Nations consistently fails in its duty to act collectively," she said, "there are times in the life of states that we are compelled to take our own action."

In the post-World War II era, the United States has, however, generally been hesitant to take unilateral military action, especially in the absence of a Congressional resolution to do so.

Wouldn't it be wonderful if Congress, which is supposed to authorize military action, actually did its job and had a real debate about what to do in Syria? Paging three Republican senators with the most serious cred on national security -- John McCain, Lindsey Graham and Jeff Flake -- to bring some legislation to the floor on this important issue. Already McCain and Graham are calling for the United States to lead a coalition to ground Assad's air force.

Members of Congress: This could be your time to step up and strap on those big boy boots that you have been keeping in the closet for so many years. More than a decade and half after 9/11, US military actions in countries such as Syria, Iraq and Afghanistan and several other Muslim nations are governed by the Authorization for the Use of Military Force (AUMF) that was passed in the days immediately after 9/11.

Clearly military action against the Assad regime falls far outside of the post-9/11 AUMF that was directed at al Qaeda and its allies. Democratic Senators Ben Cardin and Chris Murphy have warned that President Trump will need Congressional authorization to use military force.

Of course, no one is holding his or her breath for Congress to do its job, as it has largely abdicated its responsibility when it comes to the authorization of wars -- but wouldn't it be nice to be pleasantly surprised?

Whether or not Congress passes some kind of authorization on Syria, the next issue to consider is what military steps can realistically be taken there, without support from the American public for another large-scale ground invasion in the Middle East, which seems unlikely at best.

Let's go back to those safe zones for Syrian citizens. They're an admirable idea, but based on multiple discussions I have had with senior US Air Force and other military officials, implementing a safe zone in Syria would be quite complex, because it would require a "no-fly" zone to succeed. This would possibly put Russia and the United States on a collision course because Russian jets are also conducting airstrikes in Syria, while some of the planes that the Syrian air force flies are the same model as some of the Russian planes that are flying in Syrian air space.

The Russians have also given the Syrians the SA-23 surface-to-air missile system, which is one of the most sophisticated air defense systems in the world, according to US military officials.

A "no-fly" zone in Syria would also require, at least theoretically, a UN resolution, but that would be a non-starter with Russia and China.

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There are other options. In 1999, NATO did impose a no-fly zone in Kosovo without seeking a UN resolution to carry out air strikes on Serbian forces.

Trump could similarly order American warplanes to bomb Syrian airfields or take out Syrian chemical weapons facilities so Assad's planes could not drop nerve gas on their own citizens. This would be a significant escalation of the United States' role in the conflict and would put Trump on a collision course with Vladimir Putin. Such strikes would also skirt international law.

The bottom line is that on the campaign trail, it's all too easy to spout slogans that the plan in Syria is to "Bomb the s*** out of ISIS" and the like. Once you sit in the White House Situation Room, however, it's all a lot more complicated. Welcome to the NFL, Mr. President!