Senator Cory Booker is in trouble. Once upon a time he seemed like a sure thing. These days he hardly even places.

And it’s because he’s unable to tap into a base of black voters.

Cory Booker acknowledges that South Carolina, where more than half of Democratic primary ballots are likely to be cast by African American voters, is critical to his success. Julián Castro has likewise pointed to Nevada, which has the largest Latino population of the four early states, as similarly pivotal to his own chances.

But both candidates have so far failed to stand out in those states — particularly among voters of the same race and ethnicity.

New polling in South Carolina places Booker among the top five candidates, but his support among black voters is in the low single digits. In Nevada, six candidates are polling ahead of Castro with Hispanics.

Castro is about as appealing as a stale sandwich. And identity politics gimmicks aren’t a sure thing at all with a Latino electorate that is a lot broader and more complex than the media cares to admit.

But Booker’s success is particularly damning. As one of the top major black candidates in the race, he ought to be performing better.

Instead he’s underwhelming black voters the way he did black residents of Newark.