Democratic Presidential candidates have now carried 18 states (the "Blue Wall") plus DC in six consecutive Presidential elections (1992-2012). These states include 10 East Coast states stretching from DC northward to Maine excluding New Hampshire; the four Great Lakes states of Illinois, Michigan, Minnesota and Wisconsin; and the three West Coast states of California, Oregon and Washington, plus Hawaii. These states now account for 242 Electoral Votes, providing a huge Democratic base.
There are three additional states (Iowa, New Hampshire and New Mexico) currently totaling 15 electoral votes which Democrats have carried in five of the past six elections. Iowa and New Mexico went Republican in 2004, while New Hampshire went Republican in 2000. If these three states are added to the "Blue Wall," the Democratic Electoral College advantage becomes even more stark. It is challenging for Republicans to win so long as states possessing 257 Electoral Votes clearly tilt Democratic.