As part of a long profile of Karl Rove, Lemann writes:
It used to be that you could find registered Republicans and registered Democrats, or heavily Democratic and heavily Republican precincts, but that was about it; now, because XML cross-references previously incompatible databases, you can easily blend electoral and commercial information (gleaned, for example, from mail-in product-warranty cards) and identify the people in Republican precincts who are most likely to vote Democratic, or Republican voters who can be moved by a specific appeal on one issue but not by the Party's main over-all TV-ad pitch. (In the 2002 Georgia governor's race, the Republicans were able to use pro-Confederate-flag material with rural voters without the major media markets noticing.)
It's a bit absurd to blame XML. There's nothing you can do with XML now that you couldn't do before XML.