Since the emergence of the Republican Party, only two Democratic presidents, Franklin Roosevelt and John Kennedy, have been followed by Democrats, and both FDR and JFK died in office, so their successors ran as incumbents. But Republicans have not decisively won a presidential election since 1988. Since then, no Republican nominee has won more than 50.8 percent of the vote. In the six elections from 1992 to 2012, Republicans averaged 211 electoral votes, Democrats 327. Republicans lost the popular vote in five of these elections, and in the sixth, 2004, George W. Bush’s margin was the smallest ever for a reelection.

In 2012, Obama became the first president since Ronald Reagan to win two popular-vote majorities, but Obama got 3.6 million fewer votes than in 2008, a 5 percent decline. (The prior reelected president, Bush, got 11.6 million more votes in 2004 than in 2000.) Except for a small gain among those age 30 to 39, Obama lost ground among every age cohort. And in 2012, Republicans improved the share of votes they got in 2008 from men (in 2012 Obama became the first person to win a presidential election while losing the male vote by seven points), whites, young voters and Jews. And independents: John McCain lost them 44 to 52 but Romney won them 50 to 45. And by September 2013, independents were leaning Republican by 18 points, above even the 14-point advantage Republicans had in 2010.