Malawi’s last presidential election five years ago was seen as a democratic milestone. Citing significant irregularities at the polls, the nation’s highest court struck down the initial results that had kept the incumbent, Peter Mutharika, in power. The court ordered a historic rerun in 2020 that saw Lazarus Chakwera, an opposition leader, prevail over Mr. Mutharika. But now, as Malawians head to the polls for a presidential election on Tuesday, that sense of triumph seems to have evaporated. Mr. Chakwera has faced criticism for appointing allies to the commission that runs the country’s elections.