It is true that Mr. Romney would not have been elected if he only increased his percentage of Hispanic voters. Had he received 35% of the Latino vote instead of the 27% he did, Mr. Obama would still have won by roughly 4,083,340 votes. The upshot is that if Republicans hope to win the presidency in 2016, they need to do better with both white and Hispanic voters.

How much better? A higher turnout among whites (to 2008 levels) and a small increase in the GOP share of the white vote (say raising it 1% to 60%), along with a somewhat better performance among Latinos (say 35%), and Mr. Romney would have landed in the White House.

The reality is that the nonwhite share of the vote will keep growing. As the American Enterprise Institute’s Henry Olsen pointed out in a recent speech, the nonwhite vote as a share of total voters has increased in every presidential election since 1996 by 2% (much of it Hispanic) while the share of the white vote has dropped by 2% each election.

If the GOP leaves nonwhite voters to the Democrats, then its margins in safe congressional districts and red states will dwindle—not overnight, but over years and decades.