The "Hidden History" analysis shows very few cracks in the Democratic dominance among both African-American and Hispanic voters in 2012. Even among groups in the African-American community in which Republicans had displayed at least some presence from 1980 through 2004 -- men, those with a college education, and those who are married -- the GOP registered little more than trace support in each of the two contests against Obama. In each of his two races, Obama won an astounding 96 percent among African-American women, but the Democratic nominee has reached at least 90 percent among these voters in every election since 2000.

Likewise, Romney faced broad repudiation from Hispanics. Obama won nearly two-thirds of Hispanic men and more than three-fourths of Hispanic women. Each of those numbers represented the Democrats' best performance since 1996. Obama slipped somewhat from 2008 among married Hispanics, but he still exceeded the Democrats' two showings against George W. Bush. The only signs of encouragement for Republicans: During the rout, Romney gained ground from 2008 with college-educated Hispanic men (falling just short of Bush's level with them in 2004) and also attracted just over 40 percent of Hispanic Protestants, many of them evangelical social conservatives. Still, Catholics remain the largest group among Hispanics, and among them Romney drew only 21 percent, less than any GOP nominee since 1980 (except for Bob Dole in the three-way race of 1996).

All of these results map the depth of the minority-voter hole confronting Republicans -- and the daunting math they will face if they can't recover at least somewhat. If minorities reach 30 percent of the vote next time, and the 2016 Democratic nominee again attracts support from roughly 80 percent of them, he or she would need to capture only 37 percent of whites to win a majority of the popular vote. In that scenario, to win a national majority, the GOP would need almost 63 percent of whites. Since 1976, the only Republican who has reached even 60 percent among whites was Reagan (with his 64 percent in 1984). Since Reagan's peak, the Democratic share of the white vote has varied only between 39 percent (Obama in 2012 and Clinton in the three-way election of 1992), and 43 percent (Obama in 2008 and Clinton in 1996).

Changes Among Whites

To shatter that band, and return to the margins among whites they enjoyed under Reagan, Republicans would need to overcome another set of demographic changes. Just as the overall composition of the country is changing, so is the nature of the white electorate. These changes are generally displacing white groups that vote overwhelmingly Republican with white groups in which Democrats run more competitively. That dynamic makes the recent GOP performance among whites even more impressive -- but also shows the difficulty of climbing still further. The shifts are visible across several dimensions. Republicans now reliably run better among whites without a college education than those with at least a four-year degree. In 1984, those noncollege whites represented 62 percent of the total vote, while college-educated whites constituted just 27 percent. That meant working-class whites represented more than two-thirds of all white voters. But since then, according to the exit polls, the share of the vote cast by those working-class whites has declined in every election except 2000, hitting a low of 36 percent in 2012. Meanwhile, the share of college-educated whites grew through the 1990s and has fluctuated in a narrow range since. In 2012, the exit poll found, college-educated whites also cast 36 percent of the vote, marking the first time they have equaled working-class whites.