LAST week’s Republican primary in Tennessee resulted in a comfortable win for Senator Lamar Alexander over his Tea Party-backed challenger, State Assembly Representative Joe Carr. But make no mistake: The Tea Party is on a roll across the South, having mounted major primary challenges in Texas, Mississippi and South Carolina, and knocked out Representative Eric Cantor of Virginia.

The movement’s success, with its dangerous froth of anti-Washington posturing and barely concealed racial animus, raises an important question for Southern voters: Will they remember their history well enough to reject the siren song of nativism and populism that has won over the region so often before?

We often think of the typical segregationist politician of yore as a genteel member of the white upper crust. But the more common mode was the fiery populist. Names like Thomas E. Watson of Georgia, “Pitchfork” Ben Tillman of South Carolina and James K. Vardaman and Theodore G. Bilbo of Mississippi may be obscure outside the South, but for most anyone brought up here, they loom large.

In the early 20th century, these men rose on an agrarian revolt against Big Business and government corruption. They used that energy, in turn, to disenfranchise and segregate blacks, whose loyalty to the pro-business Republican Party made them targets of these racist reformers.

Their activities spawned a second wave of Southern Democratic populists, who defied federal court orders and civil rights legislation during the 1960s, even as more moderate politicians were moving on. Gov. George C. Wallace of Alabama, among others, portrayed himself as a tribune of the working class while championing segregation...