By Natasha Goenawan November 4, 2016
The November 8 election is just a few days away, and the presidential race is tightening. But what's the state of the race to control the Senate?
To answer this question, we extended our presidential prediction model to estimate the probability that either the Democrats or Republicans will be the majority party in the Senate after this election.
There are 34 Senate seats being contested this fall. Of the other 66 seats in the Senate, 34 of them are held by Democrats, 2 by independents who caucus with Democrats, and the remaining 30 are held by Republicans. Since these 66 seats are not being contested this November, Republicans can maintain majority control of the Senate by winning at least 21 seats this November. They will also have a majority if they win 20 seats and Donald Trump is elected President, since the Vice President (which would be Mike Pence in this case) can cast a tie-breaking vote in the Senate.
By the same logic, the Democrats need to win at least 14 of the 34 available seats to retake control of the Senate, and at least 15 seats if Mr. Trump is elected president.
Based on the most recent polls, we expect Democrats to win in 11 states - 10 of which we consider to be safe, and the other 1 which we think of as likely. Meanwhile, we expect Republicans to win in 16 states, 12 of which are safe and 4 of which are likely. This leaves us with 7 swing states whose outcomes will decide control of the Senate: Florida, Indiana, Missouri, Nevada, New Hampshire, North Carolina, and Pennsylvania.
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Thus, if the Democrats win at least 4 of these 7 swing states (in addition the 11 states that they are already expected to win) then they will control the Senate. On the other hand, the Republicans need to win at least 5 of the 7 swing states to maintain control of the Senate. If the Democrats win 3 of the swing states, indicating that the Republicans won 4 of the swing states, then whichever party is in the White House will also control the Senate via the Vice President's tie-breaking vote.
Due to this built-in numerical advantage, we project the Democrats as being slightly more likely than not to retake control of the Senate. Stay tuned, however - the dynamics of the race could easily change over the weekend. If they do, we'll be sure to let you know.