Western Mosul is the historic heart of one of the oldest cities in the world. Its narrow streets and alleyways are impassable for armored vehicles.

Bannon should never have had a permanent seat on the NSC, as he is a political operative, and the NSC has traditionally been a place where American interests are considered rather than narrow Republican or Democratic interests.

The hard reality is that attacks by vehicles in public places are very hard to defend against in a free and open society. The best defense against such attacks is good intelligence, and that often comes from inside the Muslim community.

We don't allow them on the streets and we don't allow motorized vehicles on our trails or in the parks. If it becomes a nuisance, the police might have an issue with it, but I don't think it's a priority for them.

When ISIS and al Qaeda have attacked or plotted attacks in the West in the past decade or so, they have invariably used hydrogen peroxide-based bombs because acquiring military-grade explosives or dynamite is nearly impossible for would-be terrorists in Western countries.

In cities like Athens, poor houses lined narrow and tortuous streets in spite of luxurious public buildings.