As these figures make clear, the number of swing districts has been on a steady decline since at least 1992, and the number of landslide districts on a steady rise. The year 2008 was a partial exception: the number of landslide districts rose slightly from 2004, but so did the number of swing districts. However, the polarization of Congressional districts became sharper again in 2012…

In addition to the sharp increase in the polarization of the presidential vote, there has also been a sharp decrease in ticket-splitting. Far fewer districts than before vote Democratic for president but Republican for the House, or vice versa. In 1992, there were 85 districts that I characterize as leaning toward one or another party based on its presidential vote. Of these districts, 27, or nearly one third, elected a member of the opposite party to the House, going against its presidential lean…

There have been other periods in American history when polarization was high — particularly, from about 1880 through 1920. But it is not clear that there have been other periods when individual members of the House had so little to deter them from highly partisan behavior.

In the partisan era between 1880 and 1920, there were extremely rapid shifts in the composition of the House. For example, Democrats went from controlling 72 percent of House seats in 1890 to 26 percent in 1894. That is equivalent to Democrats losing about 200 seats in the House relative to today’s baseline of 435 Congressional districts.