There has been much discussion about whether votes in this next election will be counted securely.
Every state has rules about what poll observers can do at the polls and how votes can be challenged. Here are the rules for your state:
Missouri The chair of the county committee of each political party named on the ballot shall have the right to designate a challenger for each polling place, who may be present during the hours of voting, and a challenger for each location at which absentee ballots are counted, who may be present while the ballots are being prepared for counting and counted. All persons selected as challengers shall have the same qualifications required by section 115.085 for election judges, except that such challenger shall be a registered voter in the jurisdiction of the election authority for which the challenger is designated as a challenger. (Mo. Rev. Stat. § 15-115.105.1).
Who may be admitted to the polling place: except election authority personnel, election judges, watchers and challengers, law enforcement officials at the request of election officials or in the line of duty, minor children under the age of eighteen accompanying an adult who is in the process of voting, international observers who have registered as such with the election authority, persons designated by the election authority to administer a simulated youth election for persons ineligible to vote because of their age, members of the news media who present identification satisfactory to the election judges and who are present only for the purpose of bona fide news coverage, provided that such coverage does not disclose how any voter cast the voter's ballot on any question or candidate or in the case of a primary election on which party ballot they voted or does not interfere with the general conduct of the election as determined by the election judges or election authority, and registered voters who are eligible to vote at the polling place, no person shall be admitted to a polling place. (Mo. Rev. Stat. § 15-115.409 for information on other individuals authorized to be in the polling place).
The identity or qualifications of any person offering to vote may be challenged by any election authority personnel, any registered voter, or any duly authorized challenger at the polling place. (Mo. Rev. Stat. § 15-115.429.1).