Fairly or unfairly, Joe Biden has been taking some heat over the fact that, while he was vice president, his son Hunter held a $50,000-a-month board position at Burisma, a Ukrainian gas firm. Democratic leaders are nervous about how his campaign for the 2020 Democratic nomination has been responding. Meanwhile, he’s slipping in the polls. Biden has survived past stumbles in part because his poll numbers are buoyed by black voters. But can that last?

After the most recent Democratic debate, Biden was criticized by some prominent African Americans for his answer to a question about how to repair the legacy of slavery in the United States. Biden’s harshest critics suggested that his rambling response telling black parents to make sure they kept the record player on at night was “the kind of paternalistic racism that has so long existed in both liberal and conservative circles.”

This certainly isn’t the first time the former vice president has been attacked for his racial rhetoric. Biden has a long history of racially insensitive statements and came under fire this year for praising the “civility” of segregationist senators he served with in the 1970s.

Nevertheless, Biden’s strong African American support kept him atop the Democratic presidential field throughout the summer. When data is averaged across seven weekly Economist/YouGov Polls from August and September, we find that 41 percent of African American Democratic primary voters selected Joe Biden as their first choice, compared with just 19 percent of whites.

The Obama effect on public opinion

Biden’s popularity with African American voters is undoubtedly due in part to his service as Barack Obama’s loyal vice president. During his presidential campaigns and his presidency, Obama’s close allies typically became more popular among both black voters and racially liberal whites who think racial inequality is due to structural forces like discrimination.

Indeed, Hillary Clinton’s popularity plummeted among African Americans and whites who were racially liberal during her 2008 presidential campaign against Barack Obama. But after Clinton joined the Obama administration, her popularity soared with both groups.

Public opinion about Biden repeats that pattern. As I noted in my book — “Post-Racial or Most Racial?” — white Americans’ racial attitudes didn’t correlate closely with how they felt about Democratic vice presidential candidates before 2008. They did with opinions about Biden.

The figure below shows that Biden was also significantly more popular with African Americans than his Democratic predecessors, Walter Mondale and Al Gore, were during their vice presidencies. Biden was rated 11 degrees warmer than Gore and 20 degrees warmer than Mondale on the American National Election Studies’s (ANES) 0-100 thermometer rating.

The ongoing Obama effect on black support for Biden

The Obama effect has continued to help Biden with African American voters. The figure below shows support for Biden among black and white Democratic primary voters in July and August, based on how favorably they rated President Obama.

Those results, which come from weekly surveys conducted in July and August by UCLA political scientists Chris Tausanovitch and Lynn Vavreck in partnership with the marketing research firm Lucid, show that Biden performed best this summer among black and white Democratic voters who rate Obama very favorably. Yet the Obama effect on support for Biden is significantly stronger for African Americans than it is for whites.

In fact, the figure above suggests that Biden does better among black voters than white voters primarily because of the Obama effect. The left side of the display shows that Biden’s support is nearly identical among black and white Democratic voters who did not rate Obama very favorably. But on the right side, you’ll see Biden performs about 10 percentage points better with African Americans who have very favorable opinions of Obama than with whites who rated Obama very favorably.

Obama remains exceptionally popular with African American voters. In the UCLA/Lucid surveys, 83 percent of black Democratic primary voters rated Obama very favorably, compared with 70 percent of white Democrats. That popularity, combined with the stronger Obama effect on black voters, adds up.

Will the ‘Obama effect’ last?

So Biden’s close connection to Obama has helped him with black voters. But that alone may not be enough to maintain his large lead with black voters in the Democratic primaries.

As political scientist Corrine McConnaughy noted in a 2016 TMC post, Andrea Benjamin’s research suggests black leaders’ endorsements of white candidates matter most when the endorsement includes information about how that candidate has worked on behalf of black voters’ interests.

Biden’s racial controversies could make it increasingly difficult for black political leaders to offer such informed endorsements — especially in a crowded primary field where most of Biden’s Democratic rivals have positioned themselves to the left of the former vice president on racial justice issues.

Moreover, the Obama effect on public opinion during Obama’s presidency was strongest on black voters who expressed the most racial solidarity with other African Americans. Prior research suggests those same voters would be least likely to support a Democratic candidate like Biden who takes tepid positions on race.

In fact, there’s already some evidence that Biden’s black support is declining. In two large UCLA/Lucid surveys conducted in early September, African American support for Biden decreased by 10 percentage points from where it was earlier in the summer (45 percent to 35 percent).

So if Joe Biden doesn’t do more to show black voters that he will represent their interests, then he certainly shouldn’t take the black vote for granted simply because of his close connection to Barack Obama.