Republicans are increasingly optimistic about the party’s chances of taking control of the Senate in November. But even if they achieve that goal, it will be difficult to maintain control of the chamber in 2016.

This year, the Cook Political Report puts just two Republican Senate seats in the “toss up” category — Sen. Mitch McConnell, Ky., and Saxby Chambliss, R-Ga. The rest of the Republican senators seeking re-election this year are considered safe.