The boos and chants of Bernie Sanders supporters and protesters competed with otherwise optimistic speakers at a gathering that was hardly unified on Monday night as the Democratic National Convention opened in Philadelphia to division that was more expected from the embattled Republican party. Photographer Ben Lowy, who has been on assignment for TIME on both political conventions, says the space was more energized— in “both good ways and bad.” “The tension was palpable,” says Lowy, who started his career as a conflict photographer.