Noam Scheiber notices  the major weakness in the administration case on Syria:
Which makes it hard not to draw an obvious conclusion: Obama has resorted to non-Syria arguments for intervening in Syria because he can’t justify an intervention on its own terms [bold mine-DL]. That was the message his speech blared on Tuesday.
Scheiber doesn’t mention this in his article, but many Syria hawks do the same thing all the time, and have been doing it long before Obama started talking about military action. They justify intervention in Syria by worrying what not attacking Syria will mean for Iran’s nuclear program, U.S. credibility (usually with Iran), U.S. “leadership” in the world, or more recently for the norm against using chemical weapons. Many Syria hawks are so preoccupied with the implications of not attacking that they have never managed to put together a coherent argument explaining why a U.S. attack would produce a better outcome for the U.S. or Syria. The non-Syria arguments are all flawed in different ways, but the main reason that they fail to persuade skeptics that intervention in Syria is merited is that they are not arguments for why direct military intervention in Syria is justified, legal, or likely to improve anything in the country or wider region. It is very difficult to win over skeptics when every other pro-intervention argument feels like an attempt to distract the audience or change the subject in order to avoid acknowledging how unnecessary and unwise an attack would be.