Clarifying for my students what distinguishes the two political parties from one another but what also serves as a unifying theme for each has been a challenge. Many of my students know that at one point in time conservative points of view were affiliated with Democrats and more liberal with Republicans, which is at odds to what one often sees today.
In the past few years, I've tried to share with them what I think is the core political value of each party. Democrats tend to believe government should reflect the will of the majority. Republicans tend to believe government should protect the minority from the tyranny of the majority. Neither of these standpoints are necessarily objectionable, though I do think the one I offer for the Republicans is more abstract than what most high school students want to hear. But, conveniently, it is a common thread that goes back to the Whigs and Federalists, forerunners of the Republicans.
Recently I was listening to the most recent installment of the very good podcast series on the presidents offered by the Washington Post. In that episode on William McKinley, Karl Rove was interviewed at length. He discussed how the 1896 election offered a clear mandate on a very old debate in American politics, about whether wealth is best created at the top (to then trickle down) or at the bottom, where it can rise up. That might be the enduring economic difference between the two parties.
Now if I could only find a coherent foreign policy thread for either party. Seems doubtful.