The wilful ignorance refers to the more credulous members of the Trump camp dismissing anything even remotely critical of the man who would make America great again as fake news or mainstream media bias.
It is difficult to counter arguments with facts when the facts are airily dismissed as lies.
I am reminded of debating evolution with fundamentalist Christians when I see this -- or Galileo's battles with religious figures over the shape of the Earth . Wilful ignorance is what it is.
Please understand that I do not characterize all Trump supporters as such -- but some among them would do Kim Jong-Un proud in their fervent and unwavering faith in Trump's judgement and deeds.