Politics fandom is a concept established and developed by Phoenix CS Andrews. It differs from political fandom, where existing fandoms (communities dedicated to cultural properties) are politicised. All fandoms are political in their own way. Politics fandom is the fandom around politics itself, individual politicians and political campaigns.
A fandom is different from a fanbase because it is intentional. People can be fans and part of a fanbase while just enjoying something on their own or talking about it to a friend. Once fans enter online and/or offline spaces dedicated to the topic, make friends with the same interests, create content related to their interests etc then they have chosen to join the community and have it become part of their identity. They are then part of the fandom.
It is easy to see therefore that joining a political party or group, talking about specific politicians, policies and campaigns, signing up to newsletters, following political accounts online and reading political biographies makes someone a politics fan and often part of the broader politics fandom if not a specific politician or party’s fandom. This is very similar to the way football fans are dedicated to teams and individuals as well as the sport, or Doctor Who fans go beyond watching every episode and even reading Doctor Who Magazine to discussing their favourite episodes online and getting snippy when their preferred Doctor or companion is disrespected.