A police vehicle can regularly be seen near the Skokie Valley Agudath Jacob Synagogue. Photo: Joe Barrett/The Wall Street Journal SKOKIE, Ill.—Descendants of Holocaust survivors and a growing Muslim population live side by side in this diverse Chicago suburb that prides itself on safety and civility. That tolerance is being put to the test as war rages in the Middle East. Skokie has long been known as a welcoming village on Chicago’s northern border, with one- and two-story homes on modest lots and good schools. A major attraction there is the Illinois Holocaust Museum and Education Center. In addition to...