When did the Republican Party become racist?

Lincoln was a Republican who stood up for civil rights. Theodore Roosevelt was a Republican who busted trusts (monopolies) and fought to conserve our natural resources. Exactly when did the Republicans switch places with the Democrats? Now it's the Democrats who stand up for minorities and the environment, and the Republicans who coddle fat-cat corporate thieves and do all they can to oppress minorities and the poor. When did the "big switch" take place?