The Democratic majority may be a short one--if it ends tonight, it will have lasted only four years, or two sessions of Congress--but it won't be the shortest in history. Republicans have actually suffered quicker exits several times in the course of U.S. history.
A handful of majorities lasted only one term of Congress (and one lasted even shorter) meaning two terms would give Democrats a tie for second-shortest in history (not counting that one exception).
Find below a list of the shortest House majorities in history, compiled at The Atlantic's request by the office of the House historian:
47th Congress - Republican Majority between Democratic Majorities of 46th and 48th Congresses
Speaker - J. Warren Keifer, December 5, 1881
Lose majority for 48th Congress (starts December 3, 1883)
51st Congress - Republican Majority between Democratic Majorities of the 50th and 52nd Congresses
Speaker - Thomas B. Reed, December 2, 1889
Lose majority for 52nd Congress (starts December 8, 1891)
80th Congress - Republican Majority between Democratic Majorities of the 79th and 81st Congresses
Speaker - Joseph W. Martin, Jr., January 3, 1947
Lose majority for 81st Congress (starts January 3, 1949)
83rd Congress - Republican Majority between Democratic Majorities of the 82nd and 84th Congresses
Speaker - Joseph W. Martin, Jr., January 3, 1953
Special Case: 72nd Congress
Following the 1930 elections, House Republicans maintained a very small majority from the previous 71st Congress but before the first session of the 72nd Congress could convene, 14 representatives-elect had died. In the subsequent special elections the Democrats gained 4 seats at the expense of the Republicans and the Democrats took control of the House, thus causing the result to have a change in majority in the House while the Senate remained in Republican control. Throughout the 72nd Congress, Democrats maintained a majority with 220 Democrats to 214 Republicans.
The shortest-lived Speakership, meanwhile, belonged to Theodore M. Pomeroy of New York, who held the gavel for only one day in 1869. The Finger Lakes Republican was elected Speaker on March 3, 1869--"as a sign of respect from his colleagues," according to the House Clerk website--holding the gavel for the final day of the 40th Congress. Republicans kept control of the House in the 41st, but James G. Blaine took over as Speaker.