You just have to look at the coverage of the Richmond Park by-election to see how we're being told to dismiss Labour out of hand, as the coverage fell into one of three Narratives:
i.) Goldsmith lost
ii.) Something something Britait
iii.) Well this proves Corbyn doesn't stand a chance
In terms of #3, it's telling that the only Labour MP that the papers seemed interesting in asking for a quote was Chuka Umunna - who is always on hand to give the papers plenty of anti-Corbyn soundbites.
Yet what wasn't reported is what actually happened in Richmond Park, and it has nothing to do with the vote in June, Goldsmith's Mayor of London campaign or even how the Tories were nakedly supporting the supposedly "independent" Goldsmith: the Lib Dems always had a strong support in Richmond Park, receiving over 20,000 votes in 1997 (when they won the seat), 2001, 2005 and even 2010 when they lost it - the only time they didn't was in the 2015 Election, where they received a little over 11,000 votes, similar to what happened in constituencies across the UK where the Lib Dem vote slumped at the Lib Dems bore the brunt of voters' wrath against Cameron. It's telling that Sarah Olney was not a member of the Lib Dems during the coalition years, so isn't tainted by association, hence the Lib Dems received 20,000+ votes once again.