Republicans are losing their hold on upper-middle-class suburbs, and the tax reform bill may be to blame. Although a number of races are still too close to call, Democrats have taken 30 seats so far — more than the 23 GOP districts they needed to seize control of the House of Representatives. In swing districts across the country, new Democratic challengers vowed to defy the Trump administration while Republican incumbents touted the benefits of tax reform and a booming economy. But the GOP’s tax reform bill may have disenfranchised fiscal conservatives in higher-income areas, since the Trump tax cuts capped...