The Americans presumably will make the defense of the capital a priority, but that may be precisely what ISIS hopes they will do, because it has other interests. “The priority, I think, for ISIS is to build their Islamic State straddling the Syria-Iraq border – that is their ultimate objective—and trying to capture Baghdad would be too big for them to accomplish; it could also sidetrack them,” says a US intelligence official based in the Middle East who is closely monitoring ISIS.

ISIS has not picked difficult battles. It has calculated carefully where it could move with the biggest impact and the least resistance. Mosul was not Stalingrad, holding out against a powerful siege; it was more like Copenhagen in World War II, folding without a fight…

Such attacks as do take place in and around Baghdad will likely aim to sow political discord and fan sectarian divisions, keeping Maliki’s government wrong-footed and on the defensive. Iraqi troops and allied Shia militiamen are holding a line north of Baghdad and trying to establish what army commanders call the Baghdad Belt around the capital. But they are making little headway mounting an offensive, relying on instead on the spotty use of airpower to take the fight into ISIS territory.