Watching them throw Sanders and then Corbyn under the bus was a wake up call for me. It's not the leftist paper it makes out to be, but strongly establishment.
The Guardian (and Luke Harding especially) have never really come clean about this, which is grating since publishing the unredacted cables is the ostensible reason for Assange's decade-long persecution and imprisonment, and the Guardian essentially followed the establishment line over this period, arguably then being complicit in the persecution of Assange for something which Harding was really responsible for.
Of course, the primary reason for Assange's persecution wasn't the release of the material per se, but to discourage him and others from further exposing govt crimes.
I also wish it were more of a leftist paper but it is what it is.