“Just let me throw this thought out. If you were an Islamic terrorist, why would you attack in the United States just when they are planning to take Syrian refugees (or maybe beginning to debate the issue)? Wouldn’t that sort of hurt your overall strategy?”
Speculation is that ISIS wants the West to close itself off to Syrian refugees to further their narrative that Islam is at war with the West. Remember these people are trying to trigger an apocalypse where they fully expect all out war to be waged against the whole of the muslim world.
Good thought.