What is a Republican party

The definition of the US political parties have changed over the years.

Acc. Wikipedia

The GOP was founded in 1854 by opponents of the Kansas-Nebraska Act, which allowed for the potential expansion of slavery into certain U. S. territories. The party supported classical liberalism, opposed the expansion of slavery, and supported economic reform. Abraham Lincoln was the first Republican president.

Parties kinda switched.

Republican Party, byname Grand Old Party (GOP), in the United States, one of the two major political parties, the other being the Democratic Party. During the 19th century the Republican Party stood against the extension of slavery to the country's new territories and, ultimately, for slavery's complete abolition. During the 20th and 21st centuries the party came to be associated with laissez-faire capitalism, low taxes, and conservative social policies.