So here's an interesting quote from Gallup Poll Managing Editor Jeff Jones I found regarding departing presidents' approval ratings: "It is common for presidents who are about to leave the White House to receive a bump in their job approval ratings between Election Day and Inauguration Day." Just something to keep in mind when looking at some of these numbers. CHJ
1964Lyndon Johnson/Hubert Humphrey (DEM) - 476,024; 61.27% (elected)
Barry Goldwater/William Miller (REP) - 296,767; 38.19%
Following the assassination of President John F. Kennedy, Lyndon B. Johnson was sworn in as president on November 22, 1963.
JFK averaged an approval rating of 70.1 percent. In his first (fraction of a) term, LBJ averaged a 74.2 percent approval rating.
Critical factors leading to LBJ’s (incumbent) 1964 nomination: Kennedy's popularity continued even after his death, helping to propel Johnson; the Vietnam War conflict had not yet escalated; LBJ’s “Great Society” agenda, a set of domestic social programs; Goldwater's status as a pioneer in the modern conservative movement (LBJ worked to paint him as an extremist); LBJ’s “Daisy Girl” campaign ad that implied Goldwater, if elected, would start a nuclear war; Goldwater voted against the 1964 Civil Rights Act (to be fair, so did a significant amount of Democrats representing the South), and black voters voted “overwhelmingly” against him in 1964 (http://www.washingtonpost.com/wp-srv/politics/daily/may98/goldwater30.htm)
Other info to keep in mind:
Johnson’s victory was very lopsided, winning 61.1 percent (more than 15 million votes). This is one of the highest popular-vote percentages in American history.
(http://www.whitehouse.gov/about/presidents/LyndonJohnson/)
1948Harry Truman/Alben Barkley (DEM) - 267,288; 51.88% (elected)
Thomas Dewey/Earl Warren (REP) - 239,714; 46.52%
Truman assumed office following the death of Franklin Roosevelt on April 12, 1945.
During his first term, Truman averaged an approval rating of 55.6 percent. However, his approval rating fell as low as 36 percent in 1948, and there was a wide expectation that Truman would lose the election (also due to a strong division within the Democratic party). Many historians dubbed his re-election as the greatest upset in American political history.
Critical factors: Truman held a strong base of Midwestern progressives; Dwight D. Eisenhower refused the nomination of either party; close race among those vying for the Republican nomination; Dewey losing votes from farmers *(see below)*; National press corps’ focus on Dewey’s “impending” victory; Truman’s verbal attacks on the 80th Republican Congress (the Dems also later recaptured Congress); Dewey’s advisers convinced him not to take any risks, leading many people to regard him as complacent; Truman embarked on an aggressive, full-fledged cross-country campaign in hopes of drawing more support; Democrats’ push for more civil rights
* This article talks about how Dewey lost a significant chunk of the rural vote in the Midwest, which has Colorado implications: “While running neck and neck with Dewey in the East, Truman was showing surprising strength in the Republican bastions in the Midwest. One farm state after another—even, of all places, Iowa—was reporting Truman pluralities.” (http://www.americanheritage.com/articles/magazine/ah/1968/4/1968_4_22.shtml)
Other info to keep in mind:
Truman was selected as FDR’s vice presidential candidate in 1944, replacing incumbent vice president Henry Wallace. Some of FDR’s key advisers did not think Wallace would be fit for president if FDR passed away. Truman reluctantly agreed. (http://www.pbs.org/wgbh/amex/presidents/video/truman_09.html#v166)
FDR was elected for four consecutive terms as president, meaning Truman’s victory marked the fifth consecutive win for the Democratic Party in a presidential election.
Truman authorized use of atomic weapons against the Japanese in August 1945, the world’s only instance of atomic warfare. Japan surrendered on August 14, 1945.