MEXICO CITY—Mexicans headed to the polls on Sunday to vote for a new lower house of Congress, state governors, and local lawmakers, in a race seen as a referendum on President Andres Manuel Lopez Obrador’s policies and efforts to shake up Mexico’s institutions. All 500 seats in the lower house, 15 state governorships, and thousands of local leadership positions are up for grabs, with some 93.5 million Mexicans eligible to vote. The elections has been tinged by the COVID-19 pandemic and vaccine rollout, as well as record criminal violence, with security consultancy Etellekt saying 91 politicians have been killed in this election cycle. Since taking office in 2018 after a landslide victory, Lopez Obrador has expanded the role of the state in the energy industry and radically cut back on the cost of government to channel resources to the poor and his priority infrastructure projects. In the process, he has …