I think this is a tricky question. One because the core value of the parties hasn’t switched. The republicans have always been the party of business the north in particular was dealing with the industrial revolution in a major way and made up over 60% of the nations GDP at the time lots of discussions about workers wages the formation of unions and the building of railroads etc... The south and the democrats on the other hand was obviously heavy agriculture based and appealed to more farmers and poor southerners and immigrants. One reason the Irish leaned so heavily Democrat is because they worked a lot of the low income jobs that nobody wanted and they thought if the slaves were free they’d move north and replace them. So you could say that their core values haven’t changed but their voting base has. by core values I’m not talking about slavery.