Chicago is bracing itself for violence this weekend, when the leaders of Nato will arrive for a high-profile summit on the shores of Lake Michigan.
As many as 10,000 protesters are expected to descend on Chicago, President Barack Obama's home city, for the event. And the city police department – which, unlike in New York or Washington, is unused to managing security for such high-profile global gatherings, and has been preparing for the event for more than a year – is now readying itself for trouble.
New riot gear has been purchased, including "sound canons" that emit noises intolerable to the human ear, and armour for the police horses. About 2,000 active-service military as well as soldiers of the National Guard are on hand to help the police department. The Secret Service is in charge of protecting the summit site itself encircled already yesterday by steel barricades.
Protesters began arriving in the city from across the US yesterday, representing a variety of interests from anarchists to anti-globalisation agitators. Above all, adherents of the Occupy Wall Street movement, which hopes to get a fillip out of the Nato weekend after a winter that has seen its media profile wane, have vowed to turn out in force.
For Rahm Emanuel, the mayor of Chicago and former White House chief of staff, the event offers peril and promise in equal parts.
Winning the right to host the summit, to be attended by the leaders of all 28 Nato countries and nearly two dozen other partner countries, must have made sense to Mr Emanuel. Altogether about 18,000 delegates, observers and journalists will descend into its streets and avenues, all paying for Chicago pizza, cars and hotels. If Chicago thinks it ranks as a global city, here is its moment to glisten.
The risks, of course, have to do with the parallel protests that spring up at gathering of government leaders nowadays. Chicago has history here, going back to the Iraq protests in 2003 which led to the arrest of about 900 demonstrators and even the 1968 Democratic Convention which is remembered only for the violent clashes between police and anti-Vietnam protesters that lasted for days – the "Battle of Chicago". That, the authorities have determined, must not be allowed to happen this time.
By way of dress rehearsal, the police have already responded to two demonstrations this week, one on Monday at the headquarters of the President Barack Obama re-election effort and another on Tuesday outside the city's main immigration court. Handfuls of arrests were made at each.
While a march is planned for tomorrow ahead of the leaders coming – a companion G8 summit for Saturday that was to have been in Chicago was relocated by President Obama to Camp David in Maryland – the big day promises to be Sunday when Occupy, which has chartered scores of buses to bring supporters from cities as far away as New York and Philadelphia, hopes to stage its biggest demonstration in months.
Whether Sunday ends with just littered streets or with broken windows or even bones will depend on both the police and the protesters.
"What law enforcement is doing, and rightly so, is hoping for the best and preparing for the worst," said Jeffrey Kramer, of private security consultancy Kroll. "There are those who are not going to be content with holding a sign."