Remember all those predictions that Democrats would enjoy a permanent electoral majority because of the large percentages President Obama won in 2008 and 2012 among two inevitably growing segments of the electorate, Hispanics and Millennials? Demography is destiny, we were told, and it is -- up to a point. But reality can change people's minds, especially those, like all Millennials and most Hispanics, who are relatively young.

You can see evidence that this is happening by comparing Obama's percentages among these groups in the 2012 exit poll with his job approval percentage in the most recent YouGov/Economist poll. This seems a reasonably fair comparison, given that Obama's 51 percent of the popular vote in 2012 tracked very closely with his 50 percent job approval in the days just before the election. Here is a table showing Obama's 2012 percentages among relevant groups, his job approval percentage in the YouGov poll and the change between the two numbers:

Group 2012 Obama support exit poll percentage 2014 Obama job approval percentage Change
All voters 51 41 -10
Ages 18-29 60 47 -13
Ages 30-64 49 42 -7
Ages 65+ 44 30 -14
White 39 35 -4
Black 93 70 -23
Hispanic 71 44 -27
Other race 58 44 -14
Less than $50k 60 43 -17
$50k to $100k 46 41 -5
More than $100k 44 46 +2


(Note: I have conflated the responses of the 30-64 age groups, weighting the responses in the non-overlapping age groups in the exit poll and the YouGov poll proportionate to their size. Also, the income categories in the two polls do not quite match. Any errors in the extrapolations are likely to be minimal and not substantively misleading.)

Tentative hypothesis: Obama approval has held up relatively well among working-age adults and among high-income voters, who tend to have strong ideological views on cultural issues. But it has slumped badly among Millennials, Hispanics and Others (most of whom are Asians). It's not hard to imagine why. Sluggish economic growth has hurt the young and Hispanics far more than others; Obamacare has young people subsidizing those age 50-64, who have much higher net worth; the Obamacare Spanish website was inoperative for two months.

More broadly, the experiences of the last five years may be undercutting Democrats' premise that big-government policies can help young people and Hispanics get ahead in life. Which is not to say that Republicans have yet presented plausible alternative policies which would enable them to do so. Appealing to the example of Ronald Reagan and the policy successes of the 1980s is not likely to have much appeal to two demographic groups whose members have zero or very little memory of that era. The numbers suggest Republicans have an opportunity to be much more competitive with these voters than they were in 2008 and 2012 -- and that the permanent Democratic majorities that psephologists, extrapolating from those years' election results, may not be as permanent as they thought.