We've heard a lot about the possibility of an Obama landslide in the Electoral College (EC), with "landslide" defined in various ways. For example, Nate Silver lists "landslide" as more than 375 electoral votes, or a margin of victory D+163.
Regardless of whether this is a realistic possibility (Nate now projects the probability at 32.75%), let's take a look at the historical margins of victory in the EC, specifically in those unusual elections where neither candidate is an incumbent.
Landslide victories are not uncommon historically, but typically they occur when one candidate is an incumbent. A losing incumbent may be burdened by unpopularity and a national crisis (Carter 1980, Hoover 1932), or a winning incumbent is popular and enjoys the advantages of incumbency (Reagan 1984, Johnson 1964, Eisenhower 1956) or is VP in a popular incumbent administration (GHW Bush 1988).
The 2008 election is somewhat unusual in that neither candidate is in an incumbent position (either as President or as VP). We have to go all the way back to 1952 for a comparable situation, when Eisenhower defeated Stevenson, then governor of Illinois.
Let’s then take a look at the margins of victory in presidential elections under these circumstances.
1952: Eisenhower (R) vs. Stevenson (D): R+353 Eisenhower
1928: Hoover (R) vs. Smith (D): R+357 Hoover
1920: Harding (R) vs. Cox (D) R+277 Harding
1912: Wilson (D) vs. T. Roosevelt (Progressive) (vs. Taft (R, incumbent)): D+347 Wilson
1908: Taft (R) vs. Bryan (D): R+159 Taft
Other examples of no-incumbents races include 1928 Herbert Hoover (U.S. Secretary of Commerce) vs. Al Smith (governor of New York), 1920 Warren G Harding (senator from Ohio) vs. James M Cox (governor of Ohio), and 1908 William Howard Taft (Secretary of War) vs. William Jennings Bryan (former House representative from Nebraska).
The victory of Woodrow Wilson in 1912 was unusual: Wilson, then governor of New Jersey, ran against Taft, the Republican incumbent, as well as against Theodore Roosevelt, who had served as president before Taft. Roosevelt, having split from the Republican party at the Convention to form his own Progressive Party, received 88 electoral votes, more than Taft, whose share of the electoral vote (8 votes: Vermont and Utah) was a historical low point for any incumbent. In fact, it has been speculated that if polling had been conducted in those days Taft might have beaten GW Bush as the least popular sitting president (although I might question this, because Taft suffered not only from his own unpopularity but also from the split in the Republican party funneling votes to Roosevelt.)
So if we include the 1916 election, then the last time a non-incumbent Democrat prevailed over a non-incumbent Republican was 96 years ago.
If we do not include 1916, then no non-incumbent Democrat has beaten a non-incumbent Republican in the last 100 years, in fact, in the last 124 years: we have to go back to the election of 1884 (!) when Democrat Grover Cleveland, governor of New York, defeated Republican Sen. James G. Blaine of Maine.
1884: Cleveland (D) vs. Blaine (R): D+37 Cleveland
Cleveland's victory was razor-thin: a mere 1047 vote margin of victory gave him New York state, ensuring an EC victory by 37 electoral votes. Cleveland was the first Democrat to win the White House since James Buchanan in 1856, before the Civil War.
Interestingly enough, the Wikipedia article on the 1884 election begins:
The United States presidential election of 1884 featured excessive mudslinging and personal acrimony.
The character attacks took place on both sides: Blaine was accused of influence-peddling, while Cleveland was revealed to have covered up the birth of an illegitimate child. Finally, Blaine sealed his own doom with a 19th century "macaca" moment (or is it Michele Ba-caca moment?), when he attended a meeting in which a Protestant minister identified the Democratic Party with "rum, Romanism and rebellion". This gaffe alienated New York City's Catholic voters and led ultimately to Cleveland's victory.
Sounds all too familiar, doesn't it?
So, regardless of whether the victory is a landslide or not, Obama appears to be on track to set another historical precedent. We should all stop a moment to think about how unique Obama is as a candidate and what an important historical juncture we now face.