Filipinos vote on Monday in midterm polls that are being seen as a crucial referendum on Rodrigo Duterte’s brutal crackdown on illegal drugs, unorthodox style and contentious embrace of China. The poll is expected to strengthen his grip on power, opening the way for him to deliver on pledges to restore the death penalty and rewrite the constitution. Duterte has found international infamy for his foul-mouthed tirades, but remains hugely popular among Filipinos fed up with the country’s dysfunction and elite politicians. He wants to bring back capital punishment for drug-related crimes as part of a crackdown on narcotics in...