Areva Martin is a CNN legal analyst, a civil rights attorney and St. Louis native. The opinions expressed in this commentary are solely her own. View more opinion on CNN.

(CNN) Many of us vividly recall the hotly contested 2016 primary race between Bernie Sanders and Hillary Clinton, whom I strongly supported. Sanders' message of fighting income inequality and pushing for Medicare for all resonated with many Democratic voters, as it does now, and after winning the New Hampshire primary he seemed to have momentum on his side. But the race inevitably shifted to the South and its heavy contingent of black voters.

Clinton benefited from her husband's popularity with black voters and pulverized Sanders in South Carolina by 47 percentage points. Sanders next got crushed on Super Tuesday, losing the southern and southwest states of Virginia, Georgia, Alabama, Tennessee, Arkansas, and Texas.

In 2020, Sanders was determined to avoid repeating that history.

He tried to increase his percentage of the black vote by blanketing Facebook with ads that highlighted his long-standing commitment to civil rights. He also talked up issues of paramount importance to the black community -- criminal justice reform and social-economic injustice. Sanders enlisted the help of influential black surrogates such as Harvard Professor Cornel West and rapper Killer Mike . He began airing a TV ad that features former President Barack Obama's past praise of him, even though he has positioned himself as the anti-establishment candidate. Former Obama aides like David Axelrod questioned the ad given that Sanders and the former President were not particularly close. In Mississippi , his campaign funded an ad campaign on black radio.

But despite all this, Sanders once again failed miserably with black voters. He got crushed, again, in South Carolina and then suffered a blowout loss on Super Tuesday.

And Tuesday night, he suffered perhaps a fatal blow by losing the three Ms -- Mississippi, Missouri, and Michigan.

So, what did Sanders do wrong this time? Well, it didn't help that on the Sunday before Super Tuesday he failed to appear at a Bloody Sunday ceremonial event in Selma , Alabama, that honors the civil rights leaders who marched across the Edmund Pettus Bridge.

Sanders compounded that mistake by canceling a rally in Mississippi . Perhaps unknown to him is that many African Americans from my hometown of St. Louis hail from the South and have deep ties to blacks in Alabama, Mississippi, and Georgia. Sanders' actions were an affront not just to those southerners, but to blacks in Missouri.

Another crucial mistake by the presidential hopeful was his failure to control the vitriol coming from his "Bernie Bro" supporters. One example: After Joe Biden trounced Sanders in South Carolina by garnering 61% of the black vote, one Sanders supporter explained Biden's victory on Twitter, saying, "People won't say it but the truth is that many voters in SC are low information voters. Which is a nice way to put it."

Since South Carolina's Democratic electorate is more than 60% African American, the perception is that the Sanders supporter was equating "low information voters" to black voters who support Biden.

In fact, exit polling shows that white voters favored Biden to Sanders by a margin of 33% to 23% and that those with advanced degrees preferred Biden over Sanders 51% to 15%.

Sanders' relentless attacks on millionaires and billionaires didn't resonate with a large segment of the black community that takes pride in the successes of black billionaires such as Robert Smith , who paid off the student loan debt of the entire 2019 graduating class at Morehouse College. Sanders doesn't seem to understand that although many African Americans suffer from an economic system stacked against them, we are economically aspirational.

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Many African Americans applaud the high achievement and success of billionaires like Oprah Winfrey, Jay-Z and Michael Jordan.

But Sanders' biggest mistake, undoubtedly, was his failure to understand the mindset of middle-aged and older African Americans.

For many of these voters, Trump's relentless attempts to dismantle Obamacare and destroy the entire legacy of the first black president -- Barack Obama -- has been an unending nightmare. The unyielding assault and systematic attack on other prominent African American leaders, like Congresswoman Maxine Waters, and the dismantling of safety net programs like the Supplemental Nutrition Assistance Program for seniors made removing Trump from office a pivotal issue for many black voters.

Joe Biden is not the perfect candidate. I take issue with many of the votes he cast as a senator and I wish his candidacy resonated more with younger voters. But Biden understands the importance of black voters and he has his pulse on the electorate. He had a regular presence in African American churches and gained the support of 100 black faith leaders in South Carolina leading up to the state's primary.

Many African Americans feel his concern for the problems plaguing our community is genuine, which is why he has scored overwhelming victories over Sanders in every state with a sizable number of black voters.

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