Ramesh Ponnuru comments in the New York Times:

Republicans are a more homogeneously conservative party today, but so too are Democrats a more homogeneously liberal party. Each party's trend has reinforced the other. As liberal Republicans joined the Democrats, conservative Democrats, feeling less at home, joined the Republican Party, making it more conservative

Indeed, he's right. The Southern Democrats, dead set against civil rights for African Americans, flocked to the Republican Party in the 1980s and 1990s. Now we see that Ponnuru sees this as an equal exchange, making the Republican party "more homogeneously conservative."

I'm glad it's clear, then, what "conservative" actually means in American politics!