Ok, here's something

This seems relevant to a dispute we've had in these parts before:

But it has been apparent for many years that the Democratic base is growing faster than the Republican base. The numbers of the unmarried and the non-churchgoing are growing faster than the numbers of married and church-going Americans. The nonwhite and immigrant population is growing at a faster rate than that of white native-borns. The Democrats are the party of the top and bottom of American society; the Republicans do best in the great American middle, which is losing ground. |David Frum|

If Frum is right, the implication is that Democrats can win by going left and turning out the base, but I'm not so sure that his understanding of the demographics is as widely shared as his rhetoric makes it sound.