Douthat fears "that the electoral college can’t long survive if electoral/popular splits start happening much more frequently":
It’s one thing to have a system that almost always reflects the will of the majority, and once every hundred years (or fifty, if you believe Sean Trende’s fascinating analysis of the 1960 popular vote) delivers a narrowly countermajoritarian outcome. It’s quite another to have one that delivers countermajoritarian outcomes every twelve years – or worse, leads to the kind of post-election nightmare scenario (a tie in the college plus an Obama popular vote lead) that David Frum imagines here. However much weight we place on state sovereignty and the importance of heterogeneity in party coalitions, we are still ultimately a democratic republic, and a system of presidential elections that seems too flagrantly and frequently anti-democratic simply cannot be sustained.
Earlier thoughts here.