They're obviously not the same party, that was SO long ago, LOL. None of the issues are the same, there's literally not a single issue you could transfer onto today besides maybe class issues/support for business interests and immigration restriction, both of which Lincoln's GOP would, of course, be to the right of Jackson's Democrats, but I'll go ahead you're not interested in that fact.
Saying "they've flipped" is so intellectually lazy, dude. Not to mention blatantly false.
I wouldn't go that far, just that a lot of people have a profound misunderstanding of the foundation of the Republican Party. Which was, it was very issue based (opposition to slavery) and not really as ideological (left vs. right) as some make it out to be. By contrast a lot of Democrats back then often accused the GOP of opposing unions because they were bigoted against immigrants, especially Roman Catholics. It wasn't like there was one party that was open minded on everybody and one party that was closed minded on everybody. It depended on the issue and the Democrats often catered to the prejudices of the "common man" because that was literally what their party was about. As the "common man" became less white that obviously became an issue so they had to pivot to include strong support of Civil Rights and what not.
And of course you've gone over the GOP largely being a party of business concerns and the social elite. That was largely the result of the jettisoning of the more liberal factions of the GOP after Reconstruction ended. If you'll notice a lot of "radicals" later became either Democrats or Mugwumps. That's not some random thing, the corruption and cronyism of the GOP under Grant and other Republicans disgusted them enough to defect.
So yeah maybe intellectually lazy, but it's not like it's some insane conclusion to make. Just misunderstanding the history of it due to pretty biased sources telling them.
