President Obama greets hip-hop artist Ludacris and others gathered for a screening of a documentary about criminal justice reform. Former attorney general Eric H. Holder Jr. is at left. (Chip Somodevilla/Getty Images)

Erik Nielson is an assistant professor of liberal arts at the University of Richmond. Travis L. Gosa is an assistant professor of Africana studies at Cornell University. Their book, “The Hip Hop & Obama Reader,” will be published in October.

In 2008, Barack Obama flipped the script on more than three decades of conventional wisdom when he openly embraced hip-hop — a genre typically viewed as politically radioactive because of its frequently controversial themes and anti-establishment ethos — in his campaign. Equally remarkable was the extent to which hip-hop artists and activists, often highly skeptical of national politicians, embraced him in return. As a result, for the first time it appeared we were witnessing a burgeoning relationship between hip-hop and national politics.

As we approach the 2016 election, however, this relationship is all but gone. Ironically, Obama — often called the first “hip-hop president” — largely is to blame.

This is especially disappointing in light of Obama’s 2008 run for office, when he encouraged artists such as Jay Z and Sean “Diddy” Combs to campaign for him, referenced rap music in his interviews and speeches, played rap at his events and openly contemplated a space for hip-hop in an Obama White House. In one of the lasting images of the campaign, Obama stood in front of an audience in Raleigh, N.C., and referenced Jay Z’s 2003 track “Dirt Off Your Shoulder” to raucous applause. In that moment, voters had every reason to believe that hip-hop indeed would have a seat at the table in an Obama administration.

Rappers certainly seemed to believe it. By summer 2008, when Obama emerged as the Democratic front-runner, we heard a barrage of songs from artists such as Nas, Jay Z, Common, Ludacris, Lil Wayne, and Young Jeezy that expressed support for Obama. At the same time, a number of performers — including KRS-One, Nas, Busta Rhymes, T.I. and Young Jeezy — publicly declared that they would vote for the first time in a presidential election, a significant and potentially risky gesture for artists who have traditionally followed iconic rap group Public Enemy’s militant call to “Fight the Power” rather than join it.

These and other rappers provided the soundtrack for, and undoubtedly helped generate, a radical shift in the electorate that propelled Obama to the White House: Youth voter turnout was the highest it had been in 35 years, and for the first time young black voters went to the polls at a higher rate than whites.

Once Obama took office, however, hip-hop all but disappeared. In 2009, for example, the Obamas launched the White House music series, which has sponsored a variety of musical performances, paying tribute to a wide range of genres, including classical, jazz, Motown and country. Hip-hop never has been included. And three years later, when his 2012 campaign released its 29-song playlist, there was not a single rap song on it.

It’s unclear what motivated the president’s retreat. Perhaps he saw hip-hop as a political liability, as it was when Michelle Obama was attacked by the right for inviting artist Common to read at a 2011 White House poetry event. Or perhaps he decided that the youth vote was a sure thing for his second election, allowing him to shift his attention to other constituencies. Whatever his reasons, it is clear that the “hip-hop president” turned his back on hip-hop.

He also turned his back on many of the issues most important to hip-hop artists and activists.

For example, he’s done little to address the war on drugs or the incarceration crisis. He’s presided over an economy in which unemployment rates are twice as high for African Americans as they are for whites. He’s been weak-kneed in the face of the gun lobby, even as urban areas such as Chicago are ravaged by gun violence. And, in what was perhaps the least hip-hop move of all, his administration made Tupac Shakur’s godmother, Assata Shakur, the first woman to appear on the FBI’s Most Wanted Terrorists List in 2013.

Hip-hop artists and activists took notice. After Obama’s first term, support from rappers began to sour as more and more became disillusioned by his backpedaling from hip-hop and his disappointing record in office. In recent months, that disillusionment has translated into vocal opposition. For example, rappers Kendrick Lamar and David Banner have attacked Obama in their lyrics for failing to address the most pressing issues facing the black community. Lil Wayne offers a similar criticism in his song “Trap House” when he raps, “Black president ain’t do nothing/We need a real n---- up in that office.”

Symbolism without enough substance has led to disappointment with Obama — and by extension, the Democratic Party. On his July 2015 song “Hillary,” Tef Poe, a prominent activist in the Ferguson, Mo., protests who has been openly critical of Obama, raps, “Hillary Clinton and Obama still telling lies” and goes on to add “F--- the entire Democratic Party.”

The changing tone from hip-hop artists appears to signal a more profound shift in hip-hop-based activism as well. A number of community organizers we’ve spoken to, many of whom work for political organizations that actively supported Obama, have become increasingly pessimistic about national politics as a vehicle for meaningful change. What they are telling us is that they will instead mobilize their members to address local, grass-roots issues.

If Obama had remained engaged with hip-hop, not only would he have fulfilled an implicit promise from 2008, but also he would have given voice to a vibrant and diverse cultural movement, one that has encouraged young people to defy the assumption that they are apathetic, uninvolved and uninterested in voting.

Without hip-hop’s support, we are left with serious questions about whether those young people, and particularly young people of color, will in fact go to the polls as they did in 2008 and 2012. While hip-hop artists and activists have proven that they can motivate these voters — a demographic that could be even more influential in 2016 — Obama has left many feeling as if national politics are, to quote rap group dead prez, no more than “politrikkks.”