Republicans under Abraham Lincoln were the party that ended slavery. Southern states began seceding before he could be sworn in. Republicans under Dwight Eisenhower were the party of Cold Warriors, and then under Ronald Reagan they became the party of ever-smaller government.
Republicans under Trump became the party that appealed to White supremacists and made protecting Confederate statues a campaign issue.
Once the party specifically pushing the importance of the Constitution and the rule of law, it is now unacceptable for party leaders like Cheney to do anything but tolerate the attempted overthrow of valid election results — the bedrock principle that makes the American political system work. The result is that a major US political party is now wedded completely to an anti-democratic ideology.