Bernie Sanders isn't the first presidential candidate to oppose reparations for slavery. All the same, the Vermont senator running for the Democratic presidential nomination has been criticized for his position over the past few days. Ta-Nehisi Coates of the Atlantic noted that Sanders promises his liberal supporters their dreams on all kinds of other issues, even if those dreams are controversial and politically infeasable. The issue of race should be no different, Coates argued.

It is, though. Recent research shows that Americans think about racial questions differently than other political issues.

In general, people with better scores on tests of intelligence are more likely to describe themselves as liberal, researchers have found. For example, they're more likely to support intrusive governmental policies intended to protect the environment, according to the new study, which was published earlier this month. They're also more likely to say that African-Americans are discriminated against and far less likely to call them stupid or lazy.

When you get down to the brass tacks of dealing with racial prejudice, though, more intelligent people seem to tunnel back into the woodwork. The new study revealed that smarter respondents are no more likely to support specific policies designed to improve racial equality - even though they are more liberal on other issues and are more likely to see discrimination as a problem.

That was the riddle Geoffrey Wodtke, the author of the study and a sociologist at the University of Toronto, was hoping to solve. To be sure, many white participants probably were conservatives who opposed the policies for reasons having nothing to do with race - skepticism about the government's ability to engineer social change or commitment to the ideal of the free market. Those reasons, though, should have been less compelling for the more intelligent respondents.

"If this is truly an issue of higher-ability whites being more opposed to fairly intrusive government interventions," Wodtke said, "they should be opposed to those across the board, at least if the principle is consistently applied."

His conclusion is that while many intelligent Americans might think of themselves as progressive, they might not be entirely prepared to stand by their stated views on race.

Wodtke examined data from the General Social Survey, which has been asking Americans about their attitudes on a range of subjects since 1972. The survey includes a short, simple test of verbal intelligence.

Among those white participants who performed poorly on the intelligence test, 46 percent described blacks as lazy and 23 described them as unintelligent. Thirty-five percent did not want black neighbors, and 47 percent would not want a black sibling, son- or daughter-in-law.

Among those who did well on the verbal test, 29 percent said blacks were lazy and 13 percent said they were unintelligent. Twenty-four percent and 28 percent opposed residential integration and interracial marriage, respectively.

Among those who scored badly, fewer than two-thirds said employers discriminate against blacks, compared to nearly four-fifths of those who did well on the test.

In other words, white respondents with better verbal intelligence scores have more favorable opinions about blacks and are less likely to blame them for their disadvantages in the economy and in society. That was even true among white respondents with the same level of education.

Yet there was no relationship between respondents' intelligence and their support for affirmative action in employment or for busing between school districts, which had the support of 12 percent and 23 percent of all white participants, respectively.

Those who scored well on the intelligence test were somewhat more likely to support laws against discrimination in housing - 55 percent as opposed to 48 percent of those who did badly on the test - but Wodtke found that difference wasn't statistically significant after he accounted for the respondents' education and other factors.

In general, researchers have found that measures of intelligence are correlated with measures of social liberalism. For his part, Wodtke found that people who did better on the verbal test were also significantly more likely to be willing to pay "much higher taxes" in order to protect the environment. They were also more likely to support environmental regulation "even if it interferes with businesses' right to make their own decisions," in the words of the questions from the survey.

To be clear, the fact that smart people tend to be liberal isn't necessarily an argument for liberalism. There are plenty of bright conservatives, of course. The correlation could reflect that some smart people have different temperaments or social circles that also affect their politics.

Moreover, these intelligent white liberals aren't especially consistent in their views. Evidently, they did not extend their confidence in government's ability to solve social problems to racial questions.

Wodtke sees more favorable attitudes toward blacks stated by more intelligent whites as the product of a changing culture. His research shows that among the oldest whites who participated in the survey - those born in 1910 - intelligence does not equate to more positive views about blacks.

Perhaps some respondents who said they opposed policies such as busing and affirmative action would have argued that race-neutral policies that disproportionately benefit black communities, such as tax credits and public assistance, are a less divisive politically and an easier way to achieve racial equity.

That possibility just raises again the question that Coates posed in his column on reparations: What is it about race-based policies that makes them so toxic?

Another figure Wodtke studied is the share of white respondents who support some form of reparations for past discrimination against blacks. Just 13 percent, on average, said they supported reparations, with no significant differences by verbal intelligence.

Asked about Coates's column, Sanders reiterated his opposition to reparations in an interview on NBC's "Meet the Press" on Sunday.

"It could be that Bernie Sanders's campaign has decided his supporters are willing to tolerate redistribution across a lot of other dimensions, except for race," Wodtke said.