November 2020 Update
While the upcoming Presidential Election garners most of the headlines, control of the U.S. Congress is also up for grabs. All 435 seats in the House of Representatives are up for election and 1/3 of the Senate seats are in play. Elections observers are not expecting Republicans to take back the House, and many are predicting that Democrats might expand their majority. As it stands now, Republicans would need to pick up 17 seats to regain the majority, but face an uphill battle given the large number of retirements from sitting members. Republicans have 33 members who have either announced their retirement, lost their primary or switched party (Rep. Justin Amash, Michigan, became a Libertarian in April). This is in contrast to House Democrats who only have 12 members who have retired or lost their primary. The most likely outcome at this stage is Democrats could pick up somewhere between one and 10 seats.
With President Trump trailing in national polls and the House seemingly out of reach for Republicans, it is vitally important to the GOP that they keep their majority in the U.S. Senate. The fate of the U.S. Senate will likely be decided by the 11 races noted below:
Alabama: Tommy Tuberville (R) running against incumbent Doug Jones (D)
Arizona: Mark Kelly (D) running against incumbent Martha McSally (R)
Colorado: John Hickenlooper (D) running against incumbent Cory Gardner (R)
Georgia: Jon Ossoff (D) running against incumbent David Perdue (R)
Iowa: Theresa Greenfield (D) running against incumbent Joni Ernst (R)
Kansas: Roger Marshall (R) running against Barbara Bollier (D)
Maine: Sara Gideon (D) running against incumbent Susan Collins (R)
Montana: Steve Bullock (D) running against incumbent Steve Daines (R)
North Carolina: Cal Cunningham (D) running against incumbent Thom Tillis (R)
South Carolina: Jamie Harrison (D) running against incumbent Lindsey Graham (R)
All of these races either are rated as toss-ups or lean Democrat/Republican. As a reminder, the current makeup of the Senate has 53 Republicans and 47 Democrats (including two independents). In 2020, there will be 35 seats up for election (including special elections in Arizona and Georgia). Democrats will need to gain three or four seats, depending on who holds the White House with the Vice President breaking ties on the Senate, in order to gain the majority.
Update provided by Bryan Cave Leighton Paisner LLP