I agree, and I will come in a moment to what I think we should be doing.
In addition to the lack of tactical and strategic bases, my third test is that the permanent defeat of Daesh in Syria requires the end of conflict, which is what allows it to thrive. Any short-term retrenchment will likely benefit the Assad regime, which is itself responsible for seven times as many civilian deaths as Daesh this year. That may mean a shift in the balance of forces, but it will bring us no nearer to resolution.