Harry Truman was pretty unpopular and it showed up in the election results. Ike had a big win. Now Eisenhower was popular and might’ve gotten elected as a Democrat but Truman’s popularity likely had a big impact. The GOP got 50.1% of the House vote, their highest percentage between 1946 and 1994. Considering that most Democrats in the South ran unopposed, and those that did get a Republican sometimes won 94%-6%, the GOP getting a majority of the House vote is pretty amazing. They won 22 additional seats. Republicans actually lost two seats in the Senate, but that’s because they had 20 seats up compared to the Democrats’ 14.
While Eisenhower had some rocky times as President he left office reasonably popular. Democrat John Kennedy got barely a majority of the vote. Because it was so close Kennedy had no coat tails. Democrats lost 20 seats in the House, but were able to only lose 1 in the senate. Considering they had 10 more senate seats up that’s pretty good.
Lyndon Johnson was very unpopular, but Hubert Humphrey managed to lose narrowly. This result was a big remarkable considering that George Wallace got a lot of previously Democratic votes. Republicans improved on their 1966 wave House percentage, but they only gained 5 seats after such a big gain two years earlier. Democrats had a lot more Senators up and the GOP also picked up 5 senate seats.
Ronald Reagan had a rocky second term, but was popular when he left office. As a result, George H.W. Bush got a big win in the Presidential election. Despite his big win, Republicans got their lowest post World War II House vote percentage when a Republican won the White House. They lost 2 House seats and 1 senate seat.
Like Reagan Clinton had a rocky second term, but left office popular. Al Gore did get the majority of the popular vote, but Democrats didn’t take the majority of the House vote and gained only 1 House seat. They did pick up 4 senate seats because Republicans had made big gains in 1994.
George W. Bush was unpopular and Barack Obama won in a landslide as a result. Democrats had their highest percentage of the House vote since 1982 and won a lot of seats. The Democrats also won 9 senate seats.
If history is a guide, Obama’s popularity will have a big impact on the election. If Obama is popular, Clinton will get anywhere from Al Gore’s small majority to a big win like George H.W. Bush. If he’s unpopular, however, she could lose in a landslide or be able to overcome that and keep the vote close. There’s no doubt she’d benefit from a popular Barack Obama and really be hurt if he’s this unpopular in 2 years.
The House is a different matter, however. Even when George H.W. Bush had a big win, Republicans didn’t do that well. It seems unlikely Republicans will get the 53%+ they got this year, but we won’t be seeing a big Democratic win. At best, they’ll probably take a small majority of the House vote and pick up 15 seats. If a Republican wins, the GOP may lose a few seats but also could pick up a few seats. Waves happen when the out party retakes the White House.
The election always occurs six years after the previous President’s first mid-term. As a result, the out party usually had more seats up. As such, the President’s party are likely to suffer anywhere from small gains, like in 1988, to losses, like in 1968. Republicans have being the out party working for them and a more seats being up working against them. The best result for the President’s party was when Democrats picked up 4 seats in 2000. A 4 seat loss for Republicans would put the senate at 50-50. On the flip side, the out party gained senate seats in 1952 even though they had 6 more seats in the election.
If Democrats are hoping for a landslide in the House and Senate vote it’d defy any historical precedent. Republicans, on the other hand, could pick up House seats. It’s not unusual for the out party to gain seats in a mid-term and then again in a Presidential election. I doubt we’ll see much in the way of gains in the 2016 election. In the House we could see a range of Republicans gaining 10 seats or Democrats picking up 15. In the senate we could see a range from Republicans picking up 1-2 or Democrats winning 4.