...Obama was spying on his campaign through their microwaves, which became fodder for late night comedy hosts and was dismissed by the likes of Lindsey Graham and Devin Nunes.
But Trump and the wingnut media stuck with it and now tens of millions of Americans think law enforcement was turned against an innocent #Trump out of partisanship and are furious about it.
This has a name:
https://thedecisionlab.com/biases/illusory-truth-effect