Back then there was a group known as the Radical Republicans. They opposed everything President Lincoln did and tried to make it harder for the states to rejoin and they tried to make the life of former slaves as difficult as possible. So since the north were the people who supported Lincoln, and the Republicans at the time hated Lincoln, the north naturally would hate the republicans. Hope I was able to help. :)
The decline in Republican support in the North during the Reconstruction Era was due to internal conflicts in the party, economic hardships, disillusionment with Reconstruction outcomes, political scandals, and shifting public sentiments post-Civil War. These factors led to many Northern voters questioning the party's effectiveness and honesty. As a result, support for Republicans decreased significantly during this time.
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