In 2014, Democrats, the majority party in the Senate, had to defend most of the seats up for election, more than a few in unfriendly territory. That year, Republicans took back control of the chamber, picking up nine seats.
Democrats are counting on a similar scenario unfolding to their advantage next year: Republicans currently have a 54-46 advantage, but of the 34 seats up in 2016, only 10 are held by Democrats.
Any outcome depends on unpredictable events over the next 10 months: the presidential race, whether the stronger candidate wins selective primaries; the effectiveness of some challengers, and changing economic or national security issues.
With that critical caveat, Democrats say there's at least an even chance they will score a net gain of four or five seats. Republicans acknowledge they may lose a couple seats, but believe they will maintain control. This is almost a mirror reflection of the analysis two years ago.