Look at Wendy Davis in 2014. All the polls claimed the race was neck and neck and the liberal media was hailing her as the great democrat savior who would turn the state blue. Then election day rolled around and she not only lost, but lost by 15 points. It was NEVER a close race, but the media knew if they leaked the real polling, democrat voters would be discouraged and sit out the election.
The reverse was true in California in 2018. The media convinced gullible California Republicans to nominate carpetbagging flakey loser John Cox (we're very familiar with his quixotic campaigns here in Illinois where he never came close to winning) as their nominee for Governor, saying over and over again that he was "within striking distance" of Gavin Newsom and could "turn California red". They bought it and eagerly nominated him over native Californians with solid conservative histories and a track record of winning elections.
The fall election season thus turned into a non-event for the Dems. Newsom easily won the office without breaking a sweat, and crushed Cox by the second biggest margin in CA history.
I wonder if the people who drank the "Cox can win" kool-aid have buyers remorse over that.