No, that is burden of proof fallacy. They are repeating widespread claims which supposedly have been proven already. Trump said it, Fox said it, Trump said it, Tucker Carlson said it, Trump said it, Alex Jones said it, Trump said it, it's all over Twitter, it's been posted here countless times... The only more substantial proof possible would be to have been in the room when whatever supposedly occurred. At least that's how they say they see it.
Appeal to ignorance would be someone who claims that the Loch Ness Monster is real while insisting it is the responsibility of anyone disputing that to try to prove otherwise.