To “sustain” somebody doesn’t mean to agree with or pledge loyalty to that person. Sustenance is provided in doing things that uplift or encourage or otherwise help. Feeling or publicly expressing allegiance to President Monson does so little to sustain him; instead, help him to accomplish his mission. President Monson worries about many things and has many goals. Alleviate his worries and advance his goals by serving neighbors and uplifting the elderly and lonely.