What I have come to see in my number crunching is not change and transformation, but continuity. Three presidents in a row have been re-elected with 49%, 51% and 51% of the vote. Over the past two decades, Democrats won four of six presidential elections and won a popular-vote plurality in a fifth. But starting in 1994, Republicans won a majority in the House of Representatives in eight of the 10 congressional elections.

That is not the result of massive ticket-splitting, as in the years from 1968 to 1988, when many Southern whites and others voted Republican for president and for Democrats in the House. On the contrary, the number of congressional districts electing a House member for one party while voting for the presidential nominee of the other declined to 26 in 2012, from 59 in 2004, and from 103 in 1992.

In fact, over the past 20 years the popular vote for House of Representatives has been a good proxy for support of the president and his party. And over most of these two decades the popular vote for the House has been fairly stable. In six of the 10 congressional elections starting in 1994, including 2012, Republicans received between 48% and 51% of the House popular vote and Democrats received between 46% and 49%. …

My conclusion: Republicans were hurt when voters doubted their competence, Democrats when voters opposed their ideology.