Summary: American presidential elections have undergone a dramatic change in recent decades.The number of swing states (which are states defined as projected to be won by less than 10% in elections in which the major parties candidates split the national popular vote) has dropped sharply, especially since 1988 and especially among our nation's largest and smallest states.

For example, only one of the 13 smallest states and only four of the 27 smallest states were swing states in 2008, much fewer than in the 1980s. We don't see this imbalance changing soon -- indeed, in 2008 only three of the smallest 13 states were within even a 15% partisanship disparity.

Furthermore, at the other end of the population spectrum in our 11 largest population states,, fewer than half were swing states in 2004 and 2008 -- down from 10 out of 11 of these states in the 1960 and the 1976 presidential elections and 8 of these states in 1988.

Looking forward, none of the 2008 non-swing states are expected to become swing states in 2012, yet some 2008 swing states may well move to non-swing state status. This decline would continue a 50-year trend summarized here.

Partisanship Disparity (P), All States, 1960-2008*

*Washington, D.C. is included in all years except 1960

Of 11 largest population states with 15 or more electors in 2008

Of 13 mid-sized states with 9 to 14 electors in 2008

Of 14 smaller mid-sized states with 5 to 8 electors in 2008

Of 13 smallest population states (including DC except in 1960) with 4 or fewer electors in 2008