At first, Barack Obama’s exhortation to black voters that their support is “not as solid as it needs to be” seems very counterintuitive. No significant demographic in American politics goes as monolithically in one direction as the African-American vote. Obama won 93% of those voters in 2012, slightly better than he did with Democrats as a whole (92%). Even John Kerry got 88% of the black vote in 2004.

Obama isn’t worried about loyalty, though — he’s worried about enthusiasm and turnout. And he should be:

President Barack Obama implored black voters to turn out for Hillary Clinton just as they did for him in both of his elections, remarking Wednesday morning that “the African-American [vote] right now is not as solid as it needs to be.”

“I’m going to be honest with you right now, because we track, we’ve got early voting, we’ve got all kinds of metrics to see what’s going on, and right now, the Latino vote is up. Overall vote is up. But the African-American [vote] right now is not as solid as it needs to be,” Obama said in an interview on the Tom Joyner Morning Show, a syndicated radio show that plays mostly R&B music and caters to a largely black audience.

Early voting among African-Americans is indeed down sharply relative to last year, a bad sign for Clinton, whose lead over Donald Trump has narrowed in recent days. In North Carolina, an all-but-essential state for Trump if he is to win the White House, the number of black voters casting ballots early is down 16 percent relative to 2012 while the number of white voters doing so has increased by 15 percent, according to the New York Times. That same Times story reported that the number of African-Americans voting early in Florida is down 10 percent compared to four years ago.

It’s not just in Florida, either. The NYT highlights the problem in Ohio, where black voters helped Obama block Republicans two elections in a row:

But in Florida, which extended early voting after long lines left some voters waiting for hours in 2012, African-Americans’ share of the electorate that has gone to the polls in person so far has decreased, to 15 percent today from 25 percent four years ago.

The problems for Democrats do not end there. In Ohio, which also cut back its early voting, voter participation in the heavily Democratic areas near Cleveland, Columbus and Toledo has been down, though the Clinton campaign said it was encouraged by a busy day on Sunday when African-American churches led voter drives across the state.

The disappointing black turnout so far could foreshadow a larger and more intractable problem for Mrs. Clinton and the Democratic Party as they rethink their place in a post-Obama era. One of the biggest uncertainties Democrats have been forced to confront in this election is whether Mr. Obama’s absence from the ticket would depress black enthusiasm, which was at historic levels in 2008 and 2012 and would have been difficult to replicate under even the best of circumstances.

The Clinton campaign believes it can close the gap, especially in North Carolina and Florida, by Election Day. And Democrats are seeing substantial gains in turnout for other key constituencies like Hispanics and college-educated women, which have the potential to more than make up for any drop-off in black voting.

But this election could determine if the Obama-era level of participation among blacks is sustainable. It could also show that the Democratic Party, which has benefited enormously from population shifts that have left the country more diverse, is facing a demographic reckoning of its own.

True, but this was also a golden opportunity for Republicans to reset the relationship with black voters — or at least to begin that process. I spent considerable time discussing this in my book Going Red, laying out how the post-Obama era would allow the GOP to stop litigating against a retiring president who remains immensely popular with these voters, and engage more productively. Rather than rely on lower turnout, Republicans had their own opportunities to make this demographic less monolithic — and Republicans at the state and local level have shown it can be done. John Kasich won 28% of the black vote in 2014, for example, and there are other examples in Going Red.

At least at the presidential level, though, Republicans have let the opportunity pass. That doesn’t translate into much good news for Democrats if the turnout stays depressed, as CNN points out, but they’re getting a boost from Latinos … maybe:

A dip in African-American turnout has knocked Democratic early voting numbers off their 2012 pace in key battleground states like North Carolina.

The trend is also evident in early vote data from other swing states that could play key roles in deciding the election, including Florida and Georgia.

More Latino voters, however, are among the more than 24.4 million American voters who have already cast their ballots — including 12.4 million in battleground states — according to a CNN analysis of the latest early voting numbers.

Republicans appear to be in better position than they were in previous presidential elections in Florida, Iowa, North Carolina and Ohio, while Democrats have improved their standing in Colorado and Arizona.

That’s not a great substitute, though. Republicans get a better percentage of Latino voters than they do with African-Americans, so although a higher turnout of Hispanic voters will help Democrats, it may not make up for the lost ground among black voters.

Unfortunately for Democrats, Obama came to the game late, and mostly as a spectator. His field operation has gone on to other goals, and Hillary Clinton has been more focused on nationalizing the election rather than building ground-up loyalty, especially in these communities. That failure could change the turnout models in ways that will not just hurt Hillary Clinton but also the down-ballot races, and upend some of the assumptions that have formed the basis of polling. A scolding on solidarity six days out from Election Day won’t change much.

The RNC has a new ad targeting disaffected African-American voters, titled “Our Choice”:

Maybe this will make a good entrée for 2018, if nothing else.