Sen. Bernie Sanders (I-Vt.) at the Democratic debate in Brooklyn on April 14. (Seth Wenig/Associated Press)

Right there, at the end of the Brooklyn debate, it happened. A whole slice of the United States, home to the bedrock foundation of the Democratic Party, was written off by a candidate for its nomination. But that wasn’t the first time Sen. Bernie Sanders (I-Vt.) or someone from his campaign has done this. It is an insult that stings more than the campaign seems to realize.

The argument from the Sanders camp is that Hillary Clinton won in conservative “deep South” states that Democrats will never win in November. To Sanders supporters, this makes a lot of sense in explaining why their progressive candidate was pushed aside by a more conservative electorate. To the African American voters who fueled the double-digit ballot beat-down Sanders suffered in those states, it is baldly dismissive. And totally in keeping with the candidate’s tone-deafness with this voting bloc, best exemplified by his campaigning with Cornel West, who famously said President Obama was “a black mascot of Wall Street oligarchs and a black puppet of corporate plutocrats.” Obama’s approval rating with blacks sits now at 89 percent. 

[‘Excuse me!’ Bernie Sanders doesn’t know how to talk about black people]

The many references go as far back as the day after the March 1 Super Tuesday primaries when Sanders’s wife, Jane, said on MSNBC, “[M]ost of the states are historically red states and are not likely to carry the day in the general election. Most of the states that Bernie has won are mostly blue states or battleground states.”

On March 28, senior strategist Tad Devine made this remarkable comment about Hillary Clinton’s primary victories. “Her grasp now on the nomination is almost entirely on the basis of victories where Bernie Sanders did not compete.” He went on to say, “Where we compete with Clinton, where this competition is real, we have a very good chance of beating her in every place that we compete with her.” And then there was this from Devine: “Essentially, 97 percent of her delegate lead today comes from those eight states where we did not compete.”

Democratic candidate Bernie Sanders spoke to African American voters at a prayer breakfast in Columbia, S.C., on Feb. 16. "When we talk about inequality, it goes without saying that the African American community is suffering even more. (Reuters)

Those states were Texas, Alabama, Virginia, Louisiana, Tennessee, Missouri, Georgia and Arkansas. Here are the stats from those states:

Texas

32-percentage-point win with 80 percent of the black vote, which was 19 percent of the total vote.

Alabama

58-percentage-point win with 91 percent of the black vote, which was 54 percent of the total vote.

Virginia

30-percentage-point win with 84 percent of the black vote, which was 26 percent of the total vote.

Louisiana

48-percentage-point win. I couldn’t find the racial breakdown anywhere. (If you have it, send it and I’ll update.)

Tennessee

34-percentage-point win with 89 percent of the black vote, which was 32 percent of the total vote.

Missouri

0.2-percentage-point win with 67 percent of the black vote, which was 21 percent of the total vote.  

Georgia

43-percentage-point win with 85 percent of the black vote, which was 51 percent of the total vote.

Arkansas

36-percentage-point win with 90 percent of the black vote, which was 27 percent of the total vote.

For good measure, let’s throw in South Carolina. The Palmetto State is high up on the Democratic primary calendar because the party voted before the 2008 election to give a bigger voice in the nominating process to Latinos (Nevada) and African Americans (South Carolina) after the Iowa caucuses and New Hampshire’s first-in-the-nation primary.

[Hardly a mystery why Clinton is clinging to Obama]

Clinton won the Feb. 27 South Carolina primary by 48 percentage points with 86 percent of the black vote, which was 61 percent of the total vote. According to the 2010 Census, African Americans are 27.9 percent of South Carolina’s population. That’s why I went slack-jawed when I heard actor and Sanders supporter Tim Robbins castigate the media by saying this at a rally on April 4 in Wisconsin.

After the Southern primaries, you had called the election. And who’s fooling who? Winning South Carolina in the Democratic primary is about as significant as winning Guam. No Democrat is going to win South Carolina in the general election. Why do these victories have so much significance?

And then at the Brooklyn debate, when asked whether he would take his nomination fight to the convention, Sanders said he would win the nomination. Then he said this:

Look, let me acknowledge what is absolutely true. Secretary Clinton cleaned our clock in the deep South. No question about it. We got murdered there. That is the most conservative part of this great country. That’s the fact. But you know what? We’re out of the deep South now. And we’re moving up.

The best synopsis of Sanders’s problem with the region was best summed up by the Atlantic’s Vann R. Newkirk II in a piece last week. “Sanders’s problem isn’t that the South is too conservative,” he writes, “but that the region is too black.” The primary voter data detailed above make that plain.

Actor Danny DeVito pumped up the thousands of Sanders's supporters in Brooklyn's Prospect Park on April 17. "We feel the Bern!" Devito said in front of an estimated 28,000 people days before New York's primary. (Reuters)

Sanders “got murdered there” for the same reason that Clinton’s victories in South Carolina and the “deep South” have so much significance. The voters in those states, in that region, are the most loyal Democratic voters. Winning their votes demonstrates broader appeal in the party and an ability to hold the coalition Obama cobbled together to win the White House. An inability to win over African American voters, who remain firmly in his corner, calls into question the ability to be victorious on Election Day.

[Why black voters remain in Hillary Clinton’s corner]

As Newkirk points out, “Fifty-eight percent of all black people and 41 percent of all people of color in the country live in the South.” He adds, “The South in many ways already reflects what the Democratic Party ostensibly seeks to be and represent moving forward.” 

That’s what’s so appalling about the constant down-talking of the “deep South.” It has been said so often that African Americans who live there (and elsewhere) can be forgiven for feeling dismissed by a man who said they’d come around once they got to know him. If Sanders, who polls show would fare better against the GOP nominee, succeeds in becoming the Democratic presidential nominee, he will rue the day he took this tack.

Follow Jonathan on Twitter: @Capehartj