And what happened in these three midterm elections — more on that in a second — mirror to varying degrees what we see playing out now: The president’s party typically faces a midterm penalty, but in the Senate, which seats are up vary by class, and the number and location of the Senate seats the non-presidential party must defend can counteract that penalty. This year, Democrats face a particularly bad Senate map. In contrast, an unpopular president will almost certainly harm his party in the House, where all 435 seats are up for election.
Now to what happened and what it could mean for 2018. In 1962, when John F. Kennedy was president, Democrats lost six seats in the House, but gained four in the Senate. As the table above shows, this four-seat net gain in the Senate is the largest presidential party pickup there in a modern midterm election. Democrats were able to minimize their House losses and even gain seats in the Senate partly because Kennedy had such a high approval rating — around 60 percent — a month before Election Day. Generally, when presidents have high approval ratings, their parties don’t perform as poorly in the House, but the president’s standing affects the overall electoral environment, which can also matter in Senate elections.