Part of what makes the 2016 presidential race so much fun is that two very astute observers looking at it through two different lenses can come up with two totally different predictions about which party is likely to prevail.

Looking at the race through a historical lens, the odds would seem stacked against Hillary Clinton (assuming that she is the Democratic nominee). In the post-World War II era, only six times has one party held the presidency for two consecutive terms, and only once has that party kept the White House for a third—a pattern that reflects what I call the “time for a change” voter dynamic. In fact, the last Democratic president directly elected to succeed another was James Buchanan, in 1856; he followed Franklin Pierce.

But looking through a demographic lens, the modern GOP's increasing reliance on a shrinking pool of older, white, and working-class voters—and its failure to attract nonwhite voters—would seem to present an enormous obstacle to the eventual Republican nominee. In 1980, when nonwhite voters were just 12 percent of the electorate, Ronald Reagan won 56 percent of white voters and was elected in a landslide. But in 2012, when nonwhite voters accounted for 28 percent of the electorate, Mitt Romney took 59 percent of white voters—and lost the presidential race by 4 percentage points. Without a total brand makeover, how can Republicans expect to prevail with an even more diverse electorate in 2016?

Although we don't yet know the identity of the future GOP nominee, we can begin to surmise what the electorate will look like next November. Cook Political Report House Editor David Wasserman recently crunched census and exit-poll data to build a statistical model of the likely electorate in each state, breaking down voters into five distinct groups: 1) whites with college degrees, 2) whites without college degrees, 3) African Americans, 4) Latinos, and 5) Asians/others.

First, the good news for Democrats: If the electorate evolves in sync with the Census Bureau's estimates of the adult citizen population (admittedly, a big if), the white share of the electorate would drop from 72 percent in 2012 to 70 percent in 2016; the African American share would remain stable at 13 percent; the Latino portion would grow from 10 percent to 11 percent; and the Asian/other segment would increase from 5 percent to 6 percent. If the 2012 election had been held with that breakdown (keeping all other variables stable), President Obama would have won by 5.4 percentage points rather than by his actual 3.85-point margin.

In addition, the group with which the GOP does best—whites without college degrees—is the only one poised to shrink in 2016. President Obama won just 36 percent of these voters in 2012, while 42 percent of white voters with college degrees pulled the lever for him. But if the electorate changes in line with census estimates, the slice of college-educated whites will grow by 1 point, to 37 percent of all voters, while the portion of whites without degrees will shrink 3 points, to just 33 percent of the total. In other words, the GOP doesn't just have a growing problem with nonwhites; it has a shrinkage problem as well, as conservative white seniors are supplanted by college-educated Millennials with different cultural attitudes.

All that said, none of these data points proves that Republicans are doomed in 2016; in fact, the GOP has some reason for optimism. First, hard math makes talk of Democrats “expanding the map” by capitalizing on favorable demographic trends in Arizona and Georgia sound premature at best. For example, Romney beat Obama by 7.8 percentage points in Georgia in 2012. Wasserman estimates that the white share of the electorate there could decline from 64 percent to 62 percent—but that change by itself wouldn't erase even a third of Romney's margin of victory in the state.

Furthermore, the shifts a Republican would need to win the Electoral College vote might be less dramatic than commonly thought. If you're searching for the “magic number” of Latinos that Republicans would need to capture the White House, you may not find one. Even if Romney had done 10 points better with Latinos in every state in 2012—winning 37 percent instead of 27 percent nationally—he would have won only one additional state: Florida. That's primarily because Latino voters tend to be concentrated in states such as California, New York, and Texas, which aren't Electoral College battlegrounds. However, if the Republican nominee were to do just 3 points better across all five segments of the electorate in 2016—a goal many GOP candidates easily surpassed in 2014—he or she would win seven more states, and 305 electoral votes.

That may be easier said than done. But the bottom line is that demographic trends, while helpful to Democrats, are no guarantee that the party will hold the White House beyond 2017.