The notion that a strike would prove catastrophic for the presidency itself is even more implausible. Come 2017, a new person will be sitting in the Oval Office, operating under the same constitutional framework in place since 1789. Having endured impeachments, assassinations, the Civil War, sex scandals, and Watergate -- among other things -- it takes willful historical illiteracy to think that the rejection of a peripheral war of choice by a co-equal branch, an eventuality the Framers anticipated, would somehow devastate the presidency. A mechanism for how that would happen is never described because there is none.

The whole notion is implausible fantasy.

What about Cohen's argument that "if Assad can thumb his nose at America anyone can, including the Islamic Republic of Iran"? Apparently, something very basic must be stated. Whatever one thinks about U.S. policy toward Iran's nuclear program, or how much it matters if they get nukes, it is safe to say this much: A nuclear Iran matters a hell of a lot more than chemical-weapon use in a Syrian civil war.

Most every Iranian understands this, but let's imagine an exception who doesn't get it:

Iranian #1: Assad thumbed his nose at America. We can too! Iranian #2: You blithering fool. America's decision about Syria wasn't a proxy for its general willingness to use force. They could crush Syria if they wanted. But the potential costs of doing so weren't worth it to them because they had no significant national interest at stake, and they would've been supporting a side in a civil war that could empower radical Islamists or trigger a wider conflict. I don't know if they'll ever strike Iran or not, but it would be foolish of us to predict based on their Syria nonintervention.

Here's Daniel Larison going over some of the same ground:

The first and most important reason to not attack is that U.S. and allied security is not threatened, and attacking Syria will not make America or any of its allies more secure. On the contrary, attacking Syria exposes U.S. allies and clients to possible Syrian retaliation and even greater regional instability, and it risks dragging the U.S. into a prolonged military engagement that very few Americans want. The proposed attack is not an act of self-defense, nor is it the fulfillment of our treaty obligations for the defense of allies. Attacking Syria would flagrantly violate international law, and would represent a significant escalation of what is still primarily an internal Syrian conflict into an international war. There is a real danger that attacking Syria could trigger a wider conflict in the region in the form of Iranian or Hizbullah attacks on U.S. installations and client states, and that would be very harmful to international peace and security, as well as potentially very disruptive to the global economy. Even if an attack did not immediately cause a direct conflict with Iran, it would sabotage any chance of a peaceful resolution of the nuclear issue, and it would make a future war with Iran that much more likely. To the extent that the “limited” strikes on regime targets do have an effect on the conflict in Syria, they are likely to intensify the conflict and cause even greater loss of life. While the strikes are being justified as an attempt to deter the government’s use of chemical weapons, there is no good reason to believe that they will be a successful deterrent. Attacking Syria would not remedy any evils, and it would needlessly inflict more harm on a country that is already suffering greatly.

Hawks have very different notions of potential costs and benefits, as evidenced by the beginning of Galston's article, where he offers this assessment:

Only now is America reckoning the full cost of the disaster in Iraq. Friends in the Middle East doubting our competence, our closest ally unwilling to stand with us in Syria, our people weary and fearful of entanglements that could prove open-ended. Little more than a decade after the Vietnam syndrome was laid to rest an Iraq syndrome has replaced it.

For some time, we've known that the Iraq War will cost trillions of dollars, that almost 5,000 Americans lost their lives there, that their families are devastated, that tens of thousands of combat veterans are wounded due to the war, some with missing limbs and others with traumatic brain injuries, and that PTSD is epidemic and suicides are epidemic. But Galston says we're only now reckoning its full costs -- now that the "costs" include reluctance to enter another war of choice. If you compare the actual costs the United States and its people bore from Vietnam and Iraq to the costs we've born as a result of a reluctance to intervene, it becomes clear that interventionists are the ones with a "syndrome."