I’ve always viewed the dynamic between Democrats and Republicans as the carrot and the stick. Democrats make their promises to mobilize the masses into voting for them. When people realize they can never actually reach the promieses dangled in front of them and get unruly, the Republicans come into power and whip the country into submission. They cause enough chaos and move the needle backwards just enough to ensure that Democrats never need to make real progress; they just need to fix the things the Republicans broke (and not in a way that they can’t be broken again).