Their rules are being enforced consistently, you just don't like their rules or agree with their conclusions.

They state pretty clearly that their policy is that they won't allow white supremacy on their board, and their conclusion is that Trump represents white supremacy. Even if they're wrong about that conclusion, they're not being hypocritical or inconsistent or capricious in their actions, with regards to that rule.

Now, if a Democratic president ever tries to ban Muslims from entering the country, or tries to end birthright citizenship, or says Mexico is sending us its rapists, or refuses to decline an endorsement from a white supremacist, or any of the other things that have made them come to this conclusion about Trump, and they fail to ban support for that Democratic president on their forum, then you will have evidence that they are not enforcing their rules consistently.

Until then, they're consistent, you just don't agree with them.