If you will indulge me, I've been looking over the figures for second term presidential elections in my spare time (ha!) lately. To me, the subject is quite fascinating.
If President Obama wins re-election to a second term, it is generally agreed that he will most certainly be the first president in American history to do so without increasing his number of popular votes and probably the first since Wilson narrowly won a second term in 1916 not to increase his number of votes in the electoral college (who dropped from 435 in 1912 to 277 in 1916). Which is to say that an Obama victory 2012 is expected to be much closer than it was 2008.
Although a few presidents have lost a re-election bid while increasing their number of votes (Martin van Buren in 1840, Grover Cleveland in 1888, and Wm. H. Harrison in 1892), none have won while obtaining fewer votes.
Presidents elected to a second terms typically expand their number of total popular votes by a good margin. Eisenhower expanded his total by 1.5 million, Nixon by a whopping 15.4 million, Reagan by 10.6 million, Clinton by 2.6 million, and G. W. Bush by 11.6 million. Will Barack Obama get more votes this time around than he did in 2008? In that election, Obama received 69.5 million votes and 365 electors.
Of course the anomaly in all this is four-termer FDR. In his bid for second term, Roosevelt followed the pattern of expanding his popular votes by 4.9 million and his number of electors rose from 472 to 523. His third and fourth term bids saw dwindling returns, but he did maintain more popular votes than he first received back in 1932.