Barack Obama and Bernie Sanders have a lot of disagreements, but there's one question on which they seem fundamentally united — they say people are telling pollsters they like Donald Trump because they are experiencing underlying anxiety about their fate in a changing economy. It's reminiscent of a theory President Obama infamously offered at a fundraiser on the campaign trail in 2008, when he said people in small Midwestern towns were becoming bitter and clinging to guns and religion because of economic decline.

It's a theory that aligns well with both Sanders's monomaniacal focus on economic inequality and Obama's recognition that as a black man, his remarks about ethnicity and identity can be unusually polarizing in a way that is not politically helpful to his own cause. But it's also a little bit nonsensical. You don't see working-class Latinos and African Americans rallying to Trump's standard, even though economic conditions are worse for nonwhites than for whites. And Trump is surging in 2015 even though today's economy is much stronger than the economy of 2012 or 2008.

A more plausible theory is to apply Occam's razor: A substantial minority of white Americans are rallying behind Trump's white ethnocentric agenda because they are — reasonably — concerned that ongoing demographic changes are threatening white people's political power in the United States.

Democrats' naive theory of Trumpism

Consider the alternative explanation Sanders offered at Saturday's Democratic debate:

What you have now is a very dangerous moment in American history. The Secretary is right. Our people are fearful. They are anxious on a number of levels. They are anxious about international terrorism, and the possibility of another attack on America. We all understand that. But you know what else they're anxious about? They're anxious about the fact that they are working incredibly long hours, they're worried about their kids and they're seeing all the new income and wealth — virtually all of it — going to the top 1 percent. And they're looking around them, and they're looking at Washington and saying, 'The rich are getting much richer. I'm getting poorer. What are you gonna do about it? What are you going to do for my kids?' And somebody like a Trump comes along and says, 'I know the answers. The answer is that all of the Mexicans, they're criminals and rapists, we've got to hate the Mexicans! Those are your enemies! We hate all the Muslims because all of the Muslims are terrorists! We've got to hate the Muslims!' Meanwhile, the rich get richer. So what I say to those people who go to Donald Trump's rallies — understand, he thinks a low minimum wage in America is a good idea! He thinks low wages are a good idea. I believe we stand together to address the real issues facing this country, not allow them to divide us by race or where we come from.

And here's Obama speaking to NPR's Steve Inskeep:

But I do think that when you combine that demographic change with all the economic stresses that people have been going through because of the financial crisis, because of technology, because of globalization, the fact that wages and incomes have been flatlining for some time, and that particularly blue-collar men have had a lot of trouble in this new economy, where they are no longer getting the same bargain that they got when they were going to a factory and able to support their families on a single paycheck, you combine those things and it means that there is going to be potential anger, frustration, fear. Some of it justified but just misdirected. I think somebody like Mr. Trump is taking advantage of that. That's what he's exploiting during the course of his campaign.

There are unquestionably some valid points in these analyses, but they fundamentally fail to account for the specific nature of Trumpism.

For example, while Trump is better-liked by Republican men than by Republican women, Republican women like him — even though women's wages haven't stagnated (and in spite of Trump's previous comments about women).

More broadly, whatever economic troubles middle-class white Americans have suffered over the past generation pale in comparison to the struggles of black and Latino Americans, who have lower incomes and far less wealth. A political movement that primarily resonated with people seized by economic anxiety would have a very different look than Trump's.

Maybe Trump supporters agree with Trump

When Joe Posner went to a Donald Trump rally to ask Trump supporters why they support his proposed ban on Muslim immigration to the United States, they were not very ambiguous: They support the ban because they think Muslims are dangerous.

A Trump fan on Twitter who labels himself @Non_PC_guy explained to me fairly clearly that he is concerned about the "browning of America" and used a hashtag that stands for Patriotic Europeans Against the Islamization of the Occident.

@mattyglesias Dems/media still kvelling @ "Browning of America". GOP in neocon dream-coma. Do they know there's a revolution? #Trump #Pegida — Non PC Guy (@Non_PC_Guy) December 21, 2015

It's of course possible that @Non_PC_guy is confused, and actually only thinks he cares about the browning of America and the Islamization of the Occident because of things liberals think are wrong with the American economy. But it's also true that 2015 marks the first time in American history that white Christians are no longer a majority of the population.

America has a black president, and he has presided over the most diverse set of executive branch appointments in history and the most diverse federal judiciary in American history. The share of the population that was born in a foreign country has reached a level not seen in generations, and even many liberals (including Barack Obama!) are expressing profound anxiety that the youngest cohort of Americans are using their clout to impose a freedom-ravishing regime of "political correctness" on the country.

These are profound demographic changes, and they have real consequences. The weight of Hispanic voters in the Democratic Party coalition is a key reason that backing a "path to citizenship" for undocumented immigrants has become a core item on the Democratic Party policy agenda. And the weight of African-American voters in the Democratic Party coalition is a key reason that Democrats are becoming much more attentive to complaints about the ways African Americans are treated in the criminal justice system. Whether you like these changes or not, they are unquestionably real and significant, and it's natural that attentive citizens would form opinions about their merits and that some people would end up on the "these changes are bad" side of the argument.

Expect more white identity politics as the white electorate shrinks

In his classic study of the politics of the Jim Crow South, Southern Politics in State and Nation, V.O. Key observed that the politics of white supremacy was strongest and most salient precisely in the states and counties that had the fewest white people. In a state like Arkansas or Texas or Tennessee that has relatively few African Americans, there was little need for an explicit white supremacy politics to ensure that white people would, in fact, be supreme. These states, not coincidentally, generated some white politicians who were racially moderate by the standards of the time and place.

In Mississippi or South Carolina, where the demographics looked different, by contrast, any hint of racial moderation would be deadly. The smaller white communities in those states were more politically vulnerable, and required a more vigorous politics of white supremacy to maintain their control.

It's natural for a toned-down version of that to play out as the United States becomes a less white country. When whites were 80 or 90 percent of the population, they did not constitute a "demographic" that could be meaningfully mobilized around white identity — instead, splits within the white community (North versus South, Protestant versus Catholic) were highly salient. But as whites become less numerous, appealing to white voters as such becomes a more viable political strategy.

Trump has surged to the top of the GOP pack by exploiting that opportunity with an unusual level of vigor and an unusual lack of subterfuge. But he's not the first politician to see the opportunity, and he certainly won't be the last. And Democrats who simply ignore the reality that people expressing concern about the changing demographic face of America are in fact concerned about the changing demographic face of America do so at their own peril.