Most polling “errors” outside of margin of error are deliberate.
Mainstream media polls are intended to do two things:
1) suppress the vote
2) justify final election results
The polling industry has faced criticism for underestimating Republicans through several cycles. Pollster Nate Cohn recently wrote that the 2022 polls could do it again. These continued misjudgments can undermine public faith in how the media covers elections. Worse still, they can affect the result of close races.
Many 2020 Senate polls underestimated Republicans. In Maine, all polls taken during 2020 showed Republican Sen. Susan Collins losing. The last poll before the election had Collins down by six points; she won by 8.6 points. Similarly, the last poll for Montana’s Senate race showed Republican Sen. Steve Daines losing by one point. Daines won by 10 points. South Carolina faced a similar problem, and Iowa, though not as dramatically, also dealt with inaccurate polling. Finally, polls in North Carolina showed Republican Thom Tillis losing. Tillis won.
Bad polls can affect a race in various ways. One of the most important concerns campaign spending. In 2020, GOP donors spent millions in races propping up incumbents who they thought were in trouble.