I have heard that probably sometime in the 20th century, the two major political parties of US switched their ideology position relatively. Is that true?

To these days, some politicians of the parties claimed the good things that were done by their own parties and criticized the bad things done by the opposite parties, disregarding the fact that these things were done before the switch (e.g. in the 19th century).

I was wondering what the switch is called in history and why the switch happened?


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