PARIS — The news, coming in the midst of countrywide celebrations for the impending Paris Olympics, was unwelcome but not unsurprising: In May, French authorities announced that they had thwarted a plot to target Olympic soccer matches. That marked the first publicly announced threat — two more have since followed — and a sign of the massive task ahead for security officials in Paris. The Olympics officially begin Friday under a dark cloud of security concerns, challenges and threats. France has a long, grim history of suffering terrorist attacks, and the combination of war and extremism in 2024 poses a...