The “press” used to alternate the blue and red between the incumbents and the challengers.
After the 1980 election, where Reagan turned the nation “red”, the press decided that it was a “most opportune moment” to stop the alternation of colours and permanently assign the COMMUNIST colour to the Republicans, and assign blue to the demonrats.
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It also helped the MSM to exacerbate the divisions in the country. You can’t foment hatred unless you permanently label your “enemy”.
And best answer is . . .
When that didn’t work the media shed its objective facade altogether.