"”The truth of the matter is that my policies are so mainstream that if I had set the same policies that I had back in the 1980s, I would be considered a moderate Republican,” - Barack Obama [0]
[0] https://thehill.com/policy/finance/137156-obama-says-hed-be-...
Obama was a very moderate Democrat for his time. If you go back in time a moderate Democrat and Republican were similar because the "center" was more reasonable. Now the "center" is just people that are ashamed that they vote Republican.