Mo. Rev. Stat. § 115.111

If any watcher or challenger interferes with the orderly process of voting, or is guilty of misconduct or any law violation, the election judges shall ask the watcher or challenger to leave the polling place or cease the interference. If the interference continues, the election judges shall notify the election authority, which shall take such action as it deems necessary. It shall be the duty of the police, if requested by the election authority or judges of election, to exclude any watcher or challenger from the polling place or the place where votes are being counted. If any challenger is excluded, another may be substituted by the designating committee chairman.