The alt-right, of which Johnson’s Conservative Party is a clear example, find *everything* a threat hence their reliance on vote-rigging, propaganda, fake news etc. The Steve Bannon rewrite of Joseph Goebbels rule-book is remarkably well thumbed in No 10; Lynton Crosby, Andy Coulson, Dominic Cummings etc all knew exactly how to smear, subvert, distort and erode democracy and accountability.
There were certainly many smears against Corbyn, sadly he just didn’t have the required skillset to fight such smears with coherent arguments and firm unambiguous positions. Sitting and endlessly dithering on a fence of ‘constructive ambiguity’ wins no friends in any camp. He was the left’s equivalent of Theresa May; a hapless leader without any relevant experience or discernible communication skills.