No one said “not to have a police force”. They said not to have a militarized unaccountable police force. Three of the nine members of the Supreme Court were appointed by Trump and three other justices are conservative. They almost always rule in his favor and have given him unprecedented power
the slogan is "Defund the police" not "eliminate the police force militarization" or "realign police funding to mental health". It is an anti-institution rally call.
The fact that Trump has appointed Justices does not make Trump's attacks on the supreme court whenever they cancel any of his radical programs less real.
You are trying to argue that he shouldn't attack the supreme court, while I am arguing destroying institutions is ingrained into populism
In my limited understanding of US politics the supreme court has a history of overriding Trump's actions as he generally favors overreach as a tactic