I think that's a part of it, but I think a bigger deal part that, when the media and political establishment saw he was electable, they also saw him as a real threat, and so they made a much more concerted effort to damage him before the next election.
That's why you got stuff like his face getting greenscreened onto a clip of voldemort on the BBC.
One thing that people underestimate is just how far to the right of the general population the media and political class is. They tend to be private school dominated, overwhelmingly drawn from southern england, and personally wealthy.