Could a Paris-like attack happen in Chicago?

We have to be concerned about it. Not just because Paris happened but because Paris is the third of a sequence of spectacular attacks that ISIS carried out in the last two months. [The others were in Ankara, Turkey, and on a Russian jetliner. This interview took place November 20.] What do those attacks have in common? They’re against civilians of the largest states in the military coalition against them. The United States is the most powerful in the coalition. And the largest, most important international cities in the United States should be the most concerned.

What’s the likelihood?

The Department of Homeland Security and others have tried to figure out the probability of these attacks like we do earthquakes. But it’s really just not possible. An earthquake is not an agent that changes its mind.

What are potential targets here?

I really don’t want to talk about specific targets. I do with the FBI. But once we start to go down that road, you’re going to give specific [ideas] that may not have occurred to some folks. It becomes more difficult to defend and secure targets.

What types of places appeal to ISIS?

Areas with large concentrations of people. Parks. Concert halls. Large restaurants. You’ll see sports stadiums [targeted] very rarely. That’s because the security that we often pooh-pooh and just think of as irritating [such as bag searches and metal detectors] is really quite good for preventing the suicide bomber from killing large numbers of people.

What can the city do to mitigate the chance of an attack?

[Immediately after Paris] is likely the safest time because we’re maximally alert. There’s going to be more of a show of police force. The real question is, can the city of Chicago take steps two months from now? Five months from now? It’s going to require more police overtime, more money for security.

How can Chicago do what you suggest, given its messy finances?

This is going to add strain to the city’s budget. But it’s a strain that our mayor is going to have to figure out. It is important to have a sustained allocation of resources toward police security in the city.

What do you think about Governor Rauner closing the Illinois border to Syrian refugees?

We don’t want to be so shortsighted about our security that we’re callous toward Muslims. That behavior is often a recruiting tool for terrorist groups. If we overreact, that can produce a whole new generation, often bigger and more ugly.