Why is red for Republicans and blue for Democrats?

Red is for Republicans and blue is for Democrats, an association that only became cemented during the 2000 election.

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Red state, blue state: How colors took sides in politics

In the U.S., Blue States Outnumber Red States, 20 to 12

Interpret this Chart. Assume Blue is for Democrats

Red State Governments Are Dominating Democrat-Led Blue Cities

Not all states are red or blue: in search of the purple states

Red Map, Blue Map The National Endowment for the Humanities

Two Americans index: Why people move to red and blue states

Texas Democrats Unveil Plan To Flip State From Red To Blue In 2020