1. It was unconstitutional. The United States was not attacked by Syria. Hence, the United States attacked Syria, not in self-defense, which means it was an act of war. The Constitution grants Congress, and NOT the President, the authority to start a war. President Trump did not consult with Congress first. There was no excuse not to do so, since there was no imminent threat against the United States, requiring such immediate action. And, in any case, the Constitution does not grant “emergency powers” to the President.
2. This was also a violation of international law. The UN Charter, to which the United States is a signatory, clearly prohibits any particular state from using force. Article 2(4) states:
“All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.”
The only exception to the prohibition of force is found in Article 51 of the Charter, which allows a member state to use force only for self-defense. Self-defense, furthermore, is construed in a very narrow manner… force can only be used by the state if the state has already been directly attacked.
It is true, however, that many governments have justified unilateral use of force in the name of a so-called “humanitarian intervention.” Nonetheless, it is far from clear (or settled) whether such an exception exists. Arguments can be made on both sides. Yet, even if one could make a sound legal argument in favor of a “humanitarian intervention,” the fact that it is such a murky concept would at the very least require some planning in advance. This attack was not well organized or planned and the future consequences of it were not properly weighed in advance.
3. Iran and Russia have been loyal supporters of the Assad regime in Syria. United States unilaterally attacking Syria, or waging war, means risking a potential conflict or military escalation with these two nations.
4. This one is pretty obvious, although many keep forgetting it. Even President Trump knows this, as he kept repeating it over and over again during the presidential debates against Hillary Clinton: Ousting Assad from Syria will leave a vacuum that will be filled by ISIS. ISIS owes most of its power and growth to the war in Syria.
Right now, and for the past six years, ISIS has been fighting against the Assad regime in Syria. They are present there. They are sometimes confused with more “moderate” rebels in Syria (whom are supported by Gulf countries that provide arms to them, among other help). With the chaos going on in Syria right now, it is almost impossible to accurately tell which group of rebels is part of ISIS or other extremist group and which group of rebels is Western-friendly.
There is a bigger threat than Assad right now: ousting him in an uncoordinated and unwise manner, as we’ve done time and time again in the Middle East, would allow ISIS to takeover the country. It could happen. It has happened (e.g. Libya and Iraq). And it will happen if we don’t learn from past mistakes.
Even our President knew all of this in 2012: