1892:
Hayes: Harrison
Cleveland: himself
B. Harrison: himself
McKinley: Harrison
Roosevelt: Harrison
Taft: Harrison
Wilson: Cleveland
Harding: Harrison
1896:
Cleveland: Palmer
B. Harrison: McKinley
McKinley: himself
Roosevelt: McKinley
Taft: McKinley
Wilson: Palmer
Harding: McKinley
Coolidge: McKinley
Hoover: McKinley (may not have voted, he was fairly apolitical at the time)
1900:
Cleveland: McKinley (appeared at a campaign rally for him)
B. Harrison: McKinley
McKinley: himself
Roosevelt: McKinley
Taft: McKinley
Wilson: Probably McKinley
Harding: McKinley
Coolidge: McKinley
Hoover: McKinley
1904:
Cleveland: Parker
Roosevelt: himself
Taft: Roosevelt
Wilson: Probably Roosevelt
Harding: Roosevelt
Coolidge: Roosevelt
Hoover: Roosevelt
F. Roosevelt: Roosevelt
1908:
Roosevelt: Taft
Taft: himself
Wilson: Probably Taft
Harding: Taft
Coolidge: Taft
Hoover: Taft
F. Roosevelt: Bryan
Truman: Bryan
1912:
Roosevelt: himself
Taft: himself
Wilson: himself
Harding: Taft
Coolidge: Taft
Hoover: Roosevelt (first time he publicly supported a candidate)
F. Roosevelt: Wilson
Truman: Wilson
Eisenhower: Taft or Roosevelt
1916:
Roosevelt: Hughes
Taft: Hughes
Wilson: himself
Harding: Hughes
Coolidge: Hughes
Hoover: Wilson? (was appointed head of the US Food Administration by Wilson)
F. Roosevelt: Wilson
Truman: Wilson
Eisenhower: Hughes
1920:
Taft: Harding
Wilson: Cox
Harding: himself
Coolidge: Harding
Hoover: Harding
F. Roosevelt: Cox
Truman: Cox
Eisenhower: Harding
1924:
Taft: Coolidge
Coolidge: himself
Hoover: Coolidge
F. Roosevelt: Davis
Truman: Davis
Eisenhower: Coolidge
1928:
Taft: Hoover
Coolidge: Hoover (reluctantly: "for six years that man has given me unsolicited advice—all of it bad.")
Hoover: himself
F. Roosevelt: Smith
Truman: Smith (possibly Hoover, given general xenophobia at the time)
Eisenhower: Hoover
1932:
Coolidge: Hoover
Hoover: himself
F. Roosevelt: himself
Truman: Roosevelt
Eisenhower: Hoover
L.B. Johnson: Roosevelt
Reagan: Roosevelt (voted for Roosevelt and Truman)
1936:
Hoover: Landon
F. Roosevelt: himself
Truman: Roosevelt
Eisenhower: Landon
L.B. Johnson: Roosevelt
Nixon: Landon
Ford: Landon
Reagan: Roosevelt
1940:
Hoover: Willkie
F. Roosevelt: himself
Truman: Roosevelt
Eisenhower: Willkie
Kennedy: Probably Willkie (Roosevelt fired his father as ambassador that year, and he was a member of America First)
L.B. Johnson: Roosevelt
Nixon: Willkie
Ford: Willkie
Reagan: Roosevelt
1944:
Hoover: Dewey
F. Roosevelt: himself
Truman: Roosevelt
Eisenhower: Dewey
Kennedy: Roosevelt
L.B. Johnson: Roosevelt
Nixon: Dewey
Ford: Dewey
Reagan: Roosevelt
1948:
Hoover: Dewey
Truman: himself
Eisenhower: Dewey
Kennedy: Truman
L.B. Johnson: Truman
Nixon: Dewey
Ford: Dewey
Carter: Truman
Reagan: Truman
Bush: Dewey
1952:
Hoover: Eisenhower
Truman: Stevenson
Eisenhower: himself
Kennedy: Stevenson
L.B. Johnson: Stevenson
Nixon: Eisenhower
Ford: Eisenhower
Carter: Stevenson
Reagan: Eisenhower
Bush: Eisenhower
1956:
Hoover: Eisenhower
Truman: Stevenson
Eisenhower: himself
Kennedy: Stevenson
L.B. Johnson: Stevenson
Nixon: Eisenhower
Ford: Eisenhower
Carter: Stevenson
Reagan: Eisenhower
Bush: Eisenhower
1960:
Hoover: Nixon
Truman: Kennedy
Eisenhower: Nixon (privately disliked him and his endorsement was lukewarm at best)
Kennedy: himself
L.B. Johnson: Kennedy
Nixon: himself
Ford: Nixon
Carter: Kennedy
Reagan: Nixon
Bush: Nixon
1964:
Truman: Johnson
Eisenhower: Goldwater (publicly disliked each other and his endorsement was lukewarm at best)
L.B. Johnson: himself
Nixon: Goldwater
Ford: Goldwater (a lukewarm endorsement)
Carter:
Reagan: Goldwater
Bush: Goldwater (was a Goldwater delegate to the RNC as well)
1968:
Truman: Humphrey
Eisenhower: Nixon
L.B. Johnson: Humphrey
Nixon: himself
Ford: Nixon
Carter: Wallace (claimed to be a supporter in 1970 gubernatorial campaign)
Reagan: Nixon
Bush: Nixon
Clinton: Humphrey
G.W. Bush: Nixon
1972:
Truman: McGovern
L.B. Johnson: McGovern
Nixon: himself
Ford: Nixon
Carter: Nixon (led the "Stop McGovern" campaign; they hate each other)
Reagan: Nixon
Bush: Nixon
Clinton: McGovern (ran the McGovern campaign in Texas)
G.W. Bush: Nixon
1976:
Nixon: Ford
Ford: himself
Carter: himself
Reagan: Ford
Bush: Ford
Clinton: Carter
G.W. Bush: Ford
1980:
Nixon: Reagan
Ford: Reagan (appeared in a Reagan campaign ad)
Carter: himself
Reagan: himself
Bush: Reagan
Clinton: Carter
G.W. Bush: Reagan
Obama: Carter
1984:
Nixon: Reagan
Ford: Reagan
Carter: Mondale
Reagan: himself
Bush: Reagan
Clinton: Mondale
G.W. Bush: Reagan
Obama: Mondale
1988:
Nixon: Bush
Ford: Bush
Carter: Dukakis
Reagan: Bush
Bush: himself
Clinton: Dukakis
G.W. Bush: Bush
Obama: Dukakis
1992:
Nixon: Bush
Ford: Bush
Carter: Clinton
Reagan: Bush
Bush: himself
Clinton: himself
G.W. Bush: Bush
Obama: Clinton
1996:
Ford: Dole
Carter: Clinton
Reagan: Dole
Bush: Dole
Clinton: himself
G.W. Bush: Dole
Obama: Clinton
2000:
Ford: Bush
Carter: Gore
Reagan: Bush
Bush: Bush
Clinton: Gore
G.W. Bush: himself
Obama: Gore
2004:
Ford: Bush (he privately said he strongly disagreed with Bush on gay marriage and the Iraq War, but I assume party loyalty was too strong)
Carter: Kerry
Bush: Bush
Clinton: Kerry
G.W. Bush: himself
Obama: Kerry (was the keynote speaker at the DNC)
2008:
Carter: Obama
Bush: McCain
Clinton: Obama (he might've voted for McCain over sour grapes, but I doubt it)
G.W. Bush: McCain (strongly disliked him for 2000, privately indicated he would've endorsed Obama if asked)
Obama: himself