Trump’s share of the California vote was lower than the lowest Republican presidential candidate in the 20th century, 31.70 percent for Alf Landon in 1936 (Franklin Roosevelt's first re-election landslide). Trump's share also was lower than George H.W. Bush’s 32.61 percent of the California presidential vote in 1992 (three-way race including Bill Clinton and Ross Perot) and Barry Goldwater's 38.47 percent of the California presidential vote in 1964 (the Lyndon Johnson landslide).
Just two second-place finishers in California presidential general elections since statehood in 1850 have garnered a smaller share of the Golden State vote than Trump in 2016 (31.62 percent): Democrat James Cox in 1920 (24.28 percent against the Warren Harding "Return to Normalcy" landslide) and Democrat Alton Parker in 1904 (26.94 percent against the Theodore Roosevelt landslide). In the late 20th century, the Democratic presidential nominee with the lowest share of the California vote was Jimmy Carter in 1980 (35.91 percent). Carter in 1980, George McGovern in 1972 (41.54 percent in California) and Walter Mondale in 1984 (41.27 percent in California) lost national landslide elections and lost California by wide margins, but fared better in California than Trump did in 2016. Trump was lower than Democrat Stephen Douglas in 1860 (31.71 percent of California vote) and American Party nominee Millard Fillmore in 1856 (32.83 percent).
Hillary Clinton won the 2016 California presidential election by the widest margin in the past 80 years (30.1 percentage points over Republican Donald Trump). Since the Golden State participated in its first presidential election in 1852, just four presidential nominees have won California by a wider margin than Hillary Clinton in 2016: (1) Republican Warren Harding in 1920 (nearly 40 percentage points over Democrat James Cox), (2) Democrat Franklin Roosevelt in 1936 (35.25 percentage points over Republican Alf Landon), (3) Republican Theodore Roosevelt in 1904 (nearly 35 percentage points over Democrat Alton Parker) and (4) Republican Herbert Hoover in 1928 (30.5 percentage points over Democrat Al Smith).
(One caveat: Republican President William Howard Taft received a small number of votes in California as a write-in candidate in 1912. Taft was the party’s official national nominee that year,but his name did not appear on the California ballot. Former Republican President Theodore Roosevelt's electors appeared as the “Republican” slate on the 1912 California presidential ballot because the California state Republican Convention chose Roosevelt over Taft as the state’s official Republican candidate for the 1912 general election ballot. The California Secretary of State attempted to list Taft on the ballot, but the California Attorney General advised against it. Taft challenged Roosevelt all the way up to the California Supreme Court in his failed attempt to be listed on the November 1912 presidential ballot.)