The point of this thought experiment is to illustrate what Trump has already accomplished: he has, to no small degree, hamstrung our enemies. A large-scale tactical success for them would risk strategic disaster. Trump campaigned on the strategic advantage of unpredictability. The popular response to a large attack would, simply put, elevate him. That is a thing that the jihadists devoutly want him not to have, for reasons that should be obvious.
This is true because of the asymmetric nature of our conflict. We are the conventional power, clearly superior in resources and technology. They are the guerrilla force, relying on concealment, surprise, and a low-intensity conflict to neutralize those advantages. But they also rely on occasional spectacular victories to maintain recruitment, retention, and a fanatical level of devotion to their cause, which is essential when suicide is a major element of your offensive efforts. Trump has effectively denied them one of those without risk of losing the other – and made Americans safer in the process.