With Democrats currently holding a 53-47 majority, the Republicans would cut into that by picking up the Democratic-held seats in Missouri, North Dakota, Nebraska and Montana, while Democrats would win the seat of retiring Sen. Olympia Snowe (R-Maine). This pickup assumes that former Maine Gov. Angus King (I) caucuses with the Democrats, which he is widely expected to do despite being publicly noncommittal.
Republican Sens. Dean Heller (Nev.) and Scott Brown (Mass.) would hold on in close contests, while Democrats would hold competitive open seats in Virginia, New Mexico and Wisconsin. Democratic Sens. Sherrod Brown (Ohio) and Bill Nelson (Fla.) would also keep their seats under this scenario.
Arizona and Indiana would stay in Republican hands, while Democrats would hold on in Hawaii.
This scenario would most likely be coupled by an excruciatingly tight presidential contest between Romney and President Barack Obama. With the economy slow to recover but with Obama still seen as a likable figure, that’s not hard to imagine. National polling has the two candidates within the margin of error, and the list of competitive states remains lengthy.
Among the other plausible ways the Senate could end Nov. 6 split: Democrats pick up Massachusetts but lose Virginia, where the Senate results could end up following the top of the ticket.
However, it’s more difficult to see how the parties split the Senate if Democrats are able to hold on in Montana, a difficult state for Democrats where Sen. Jon Tester (D) is running a strong campaign but facing a tough challenger in Rep. Denny Rehberg (R).
While the presidential race has more of an effect on House races in general, a Tester win in Montana — where Obama is not competing — could portend Democratic success with Senate seats in more competitive presidential states such as Wisconsin and Virginia. Of course, being open seats, the dynamics of those contests could differ from a state such as Montana.
Nothing is certain, anything can happen, and Senate strategists will likely be entertaining many of these scenarios until Election Day.