Former Illinois state Rep. Robin Kelly, whose campaign received a $2 million boost from New York City Mayor Michael Bloomberg, easily captured Tuesday’s special election to replace former U.S. Rep. Jesse Jackson Jr. The win for the Matteson Democrat was widely expected as the Chicago-area district, which Jackson represented from 1995 until late last year, has been a Democratic stronghold for roughly six decades. Kelly emerged from a crowded field in the February primary by focusing heavily on anti-gun efforts and was helped by ads from Bloomberg’s super PAC. Kelly, 56, vowed to become a leader in the federal fight...