He means people outside the US being nasty about Trump.
It's what Hitler would have done had the people of Germany been able to access what the rest of the world thought of them. Remember how much of a shock it was to a lot of Germans to realise they were the baddies.
If you can't prevent the information being disseminated (although controlling Twitter and Facebook is a good headstart) then the next best thing is to ensure the people that matter (i.e. your own country) believe it is all "fake news".
So that is what Vance is doing here.
And as always remember who his audience is. It's not us. It's the people who will believe this sort of shite because they want to believe. Again a testament to the corrosive power of organised religion. If you are going to believe in fairy stories, then you are prime material for believing any old nonsense.
Putins pretext for invading Ukraine was to "rid it of Nazis". Let's not be surprised when the US pretext for attacking Europe is the same.