RecruitingPhase 2Drug trialTrial Utilizing Metronidazole to Optimize the Microbiome of Rectal Adenocarcinoma Undergoing Neoadjuvant TherapyTo learn if adding metronidazole to standard therapy can decrease populations of Fusobacterium nucleatum (F. nucleatum) and other anaerobes (small organisms that cause infections) in participants with rectal cancer receiving neoadjuvant therapy, compared to neoadjuvant therapy alone.