FOX has probably already said multiple times that Hitler was a socialist; after all, the party was the "National Socialist" party.
As for Sanders, while he self-describes as a democratic socialist, he's really a pretty bog-standard social democrat who probably wouldn't look much out of place in UK's Labour or Germany's SDP.
And as for the Democratic Party being left of centre, that's the Washington centre. The popular centre on economic and foreign policy issues is well to the left of most elected Democrats.