If Georgia Democratic Senate candidate Jon Ossoff ultimately prevails over incumbent GOP senator David Perdue (and at this moment the issue is still in doubt), the Democrats will control the White House, the Senate, and the House of Representatives, which has occurred in five different periods since World War II.
One possible comfort for members of the GOP if they lose the Senate: in the last forty years, the two times the Democratic Party has controlled all three entities it has only lasted for two years: 1993-1994, 2009-2010. In the ten years before that, they controlled all three entities for four years: 1977-1980.
Following the tenure of Franklin Delano Roosevelt, when the Democrats held control of those three entities for his entire twelve-year tenure (1933-1945), the Democrats held control between the years 1949-1952, 1961-1968, 1977-1980, 1993-1994, and 2009-2010. The GOP has controlled the three entities in 1953-54, 2003-2004, and 2016-2017.
In 1949, the Democrats held a whopping 54-42 lead in the Senate, with a 92-vote lead in the House. That shrank to a tiny one-vote Senate lead and 35-vote House lead in 1951. In the 1952 election, the GOP, led by Dwight Eisenhower, won the White House, the Senate, and the House.
The next time the Democrats were in control was in 1961, after the election of John F. Kennedy. Their Senate lead was massive: 64-36; (they had gained that huge lead in the 1985 elections) their House lead was 89 votes. They essentially kept similar numbers through the presidency of Lyndon Johnson; Richard Nixon’s election in 1968 gave the GOP the White House, but the House of Representatives was in control of the Democratic Party for an astonishing forty years, from the 1954 elections until the 1994 elections.
The election of Bill Clinton in 1992 gave the Democrats control of all three entities for the first time in 24 years; they controlled the Senate by a large margin, 57-43, and held a sizable 82-vote lead in the House.
The 1994 election, though, was a historic reversal; the GOP swept 56 seats in the House, turning what had been an 82-vote deficit into a 30-vote majority. After the election of 2000, the GOP gained control of the White House with the election of George W. Bush, still held control of the House, and actually would have controlled the Senate, which had wound up in a 50-50 tie, but Senator Jim Jeffords of Vermont switched from the Republican Party to become an independent, received his committee assignments from the Senate Democrats and became chairman of a standing committee, thus denying control to the GOP.
The GOP did gain control in 2003, garnering a three-vote Senate lead and a mere 12-vote majority in the House. The four years between 2003-2007 were the longest the GOP had controlled all three entities since before Roosevelt.
In 2012, Barack Obama’s election meant the Democrats gained control of all three entities; the Democrats held a huge 60-40 majority in the Senate and a 79-vote lead in the House. That only lasted two years; in 2016 the GOP gained control of all three entities; that only lasted two years.