poisoning the well - discrediting your opponent to an audience in advance, in order to encourage dismissing any future claims or accusations they may make against you.
: Trump preemptively discredits the Mueller investigation, two weeks before its findings are released, as nothing more than a group of angry, biased prosecutors pursuing their own agendas.

poisoning the well - discrediting your opponent to an audience in advance, in order to encourage dismissing any future claims or accusations they may make against you.
: Trump preemptively dismisses any current or future negative polling data for him as nothing more than biased news outlets pursuing their own agendas.