A year ago, Tony Estanguet, head of the Paris Olympics, boldly declared that France’s capital would be “the safest place in the world.” When the Games open this Friday, Estanguet’s confident forecast looks less far-fetched now, with squadrons of police patrolling the streets, fighter jets and soldiers primed to scramble an erected, iron-like curtain on both sides of the River Seine that will star in the opening ceremony. France’s vast police and military operation is in large part because the July 26–August 11 Games face unprecedented security challenges. The city has repeatedly suffered deadl…