We're up to our 20th midterm election update. Here's what history tells us about midterm elections:
Since the advent of the current two-party system, we've averaged the President's party losing 4 Senate seats and 30 seats in the House. If that happens this year Democrats would retake control of both chambers of Congress. Democrats only need to flip two Senate seats to retake control and they need 24 seats in the House. History is on the side of the Democrats reclaiming control going into this cycle.
There are only three times that the incumbent President's party has gained seats, first in 1934 during FDR's first term, then in 1998 during Bill Clinton's second term and lastly in 2002 during George W. Bush's first term. Thus only 3 out of 39 midterm elections have resulted in the President's party gaining seats. Here's another way of looking at it. History suggests there's a 92% chance Democrats will gain Congressional seats this year. The question becomes how many. That's where it's helpful to look at the history of generic ballot polls and outcomes. These are the past four cycles:
The first number is the average generic ballot polling on Election Day and the second is the actual result:
2014: GOP +2.4 - GOP +5.7 = GOP +3.3%
2010: GOP +9.4 - GOP +6.8 = GOP -2.6%
2006: DEM +11.5 - DEM +7.9 = DEM -3.6%
2002: GOP +1.7 - GOP +4.6 = GOP +2.9%
Polls average being off by about 3%. However, history has shown that the party with a generic ballot advantage has always performed the best in the midterm elections. This is equivalent to a "home field advantage" and represents about a third of the picture when attempting to determine the likely outcome of elections. As of today, the generic ballot says DEM: +7%.
After a big gain for Democrats in the prior week, surging to two-month highs, Democrats gave back one point on the generic ballot over the past week. Still, a seven-point advantage is solid at this stage for Democrats and would doubtless lead to gains in November if this were margin to hold. It is just short of wave territory however and based on the states that've already held primaries we're continuing to see that Republicans are extremely well positioned for many key Senate races. Gov. Scott is leading in Florida and Kevin Cramer is leading in North Dakota. Both of those represent gains for Republicans in November. Were those wins to happen it'd be almost certain that Republicans would be able to hold the Senate.
Democrats have led on the generic ballot by an average of 3% to 12% thus far in 2018. Anything in the 8%+ range would likely produce a "wave" type of election. Anything in the 4% or under range would likely result in Republicans retaining complete control. At 7%, based on current data from this cycle, Democrats would be positioned to pick up 25+ seats in the US House and, based on the latest data in the Senate, there would likely be no net change. As of today, Democrats would gain control of the US House, but Republicans would retain control of the US Senate.
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