But wouldn't that cost McCain his advantage among racists? In the current issue of TNR, John Judis estimates that Obama's race could cost him as much as "15 to 20 percent of Democrats or Democratic-leaning Independents," and Politico's Roger Simon thinks the race vote is worth upwards of 15 percent among the general electorate.
By adding diversity to his ticket, McCain would just jeopardize his hold on these voters, while reaping few rewards. It's not like McCain can out-diverse Barack Obama: Those committed to voting for a black candidate will probably stick with the one at the top of the ticket. Meanwhile, racism knows no hierarchy--a black v.p. might dampen the enthusiasm of erstwhile racist McCain voters, while doing nothing to cut into Obama's support.
Thus, McCain would risk alienating the voters most constitutionally opposed to Obama; dilute the glue that's held together the Nixon coalition for forty years; and forego a perennial Republican advantage at precisely the time when it could prove most potent--all in service of a chimeric, squishy concept that that many Republicans hate, diversity.
McCain is currently in the doghouse with many race-conscious wingers for pushing immigration reform. It would be politically safe--though clearly not moral or progressive--for McCain to keep mending fences on that front, rather than bow to elite pressure for a colorized ticket.