Anybody that tells you that House seats go up and down based on the idea that America is unhappy with the President or the party in power is telling you at most half of the story.
In 1946 the Republicans picked up 55 seats due to unhappiness with President Truman. Two years later the Democrats picked up 75 seats even though Truman won the election by one of the smaller margins of the 20th century. The Republicans then picked up 28 seats two years later. Unhappiness with Truman? Perhaps. The Democrats’ seats in 1951-1952. were just a few less than 1945-1946. When Eisenhower got elected the Republicans picked up 22 seats. The Democrats picked up 19 two years later.
America was hit with a recession in 1958. People blamed Eisenhower and the Republicans lost 48 seats that year. John F. Kennedy, a Democrat, was elected two years later. Yet the Republicans picked up 21 seats. Johnson had big coattails in 1964, picking up 36 seats for his party. Two years later the Republicans picked up 47 seats. This left the representation split in the same range it’d been a few years earlier.
Between 1944 and 1994 only once did were Democratic seats outside of the 232-263 range two sessions in a row. Democrats got a big bump during Watergate and didn’t decline to that range until Reagan was elected three sessions later. There was an equilibrium in seat distribution. Any surge due to Presidential or party popularity was followed by a similar decline.
The first time there was no decline after a surge was the 1994 election that Republicans gained 54 seats. A new equilibrium was established where the Republicans had between 221 and 232 seats while the Democrats had between 202 and 212.
The Democratic gains of 52 seats could establish a new equilibrium but polls in many Republican leaning districts indicate that likely isn’t true. If the Republicans win 43 seats this year they’ll once again be in the 1994-2006 range.
Redistricting may result in the Republicans taking additional seats in 2012, but it’s worth noting that since World War II none of the top ten gains were in years following redistricting.