Since 1856, there were 40 D vs. R elections
23 republican victories
17 democratic victories
16 open seat elections
10 open seat elections in which the party of the president lost
6 open seat elections in which the party of the president won
12 republican victories in open seat elections
4 democratic victories in open seat elections
24 elections in which the incumbent president was running for the reelection
17 victories of the incumbent president
7 losses of the incumbent president
14 national popular vote margins <5% (including 3 negative margins)
11 national popular vote margins between 5% and 10%
15 national popular vote margins >10%
GOP incumbents were defeated in 1892, 1912, 1932, 1976, and 1992. Dem incumbents were defeated in 1888 and 1980-- and only in 1980 did the GOP candidate win the PV in unseating the incumbent.
