The issue of race in America dominated Thursday as some of the top contenders for the Democratic Party’s presidential nomination, addressing a group of black journalists in a South Florida forum, portrayed racism as an existential crisis ripping the country apart.

The National Association of Black Journalists hosted U.S. Sens. Cory Booker and Bernie Sanders, and South Bend, Indiana, Mayor Pete Buttigieg for half-hour question-and-answer sessions as part of a national convention at the J.W. Marriott Miami Turnberry Resort & Spa in Aventura.

The discussion touched on economics and healthcare, and the candidates’ own personal experiences, but frequently focused on domestic terrorism and hate-based politics in the wake of a massacre of Hispanic immigrants over the weekend in Texas.

“We need to be really clear that this whole country is in danger by white supremacy,” said Buttigieg.

When asked if he believes President Donald Trump is a white supremacist, Buttigieg said: “I do.”

“At best he is emboldening and empowering people with that ideology. At worst he is propelling it intentionally,” Buttigieg said. “I can’t see into the guy’s heart.”

Already unavoidable on the campaign trail, issues of race and ethnicity emerged as a crucial theme for presidential candidates this week after a gunman believed connected to a manifestodenouncing a Hispanic “invasion” targeted Mexican immigrants at a Walmart in El Paso, Texas. In recent days, the question of how to confront the spread of domestic terrorism — and the discourse around the president’s embrace of nationalist values and anti-immigrant rhetoric — have become frequent themes in speeches and interviews with the Democratic Party’s two dozen candidates.

Booker, of New Jersey, spoke Thursday about the Charleston church where in 2015 a white supremacist shot and killed people with whom he’d just prayed. Booker gave a speech Wednesday from the church’s lectern, during which he made references to Trump’s border wall and its connection with nationalist values.

“When a white supremacist entered that church and killed nine people, he wasn’t simply targeting individuals. He was targeting the heart of our community like church burners and bombers of decades past,” Booker said Thursday at the NABJ conference. “The truth is, white supremacism has always been a problem of our American story. Do not let the Disneyland version of our history be the one that’s paramount.”

Trump, who in 2017 defended the “very fine people” who protested the removal of a confederate statue in Charlottesville alongside neo-Nazis before a driver plowed his car into a crowd of anti-nationalist protesters, split his time Wednesday between visiting shooting victims in El Paso and Dayton, Ohio, and attacking his opponents and the media. From the White House lawn, he told reporters that he is concerned about all types of supremacism.

But the president has declined to condemn white nationalism in the past, even once referring to himself as a “nationalist” during an October campaign rally in Texas for Sen. Ted Cruz ahead of last year’s midterm elections. He also spent the last month stoking racial divisions by telling four freshmen Democratic congresswomen of color to “go back” to the “crime-infested places from which they came,” and blistering U.S. Rep. and former Congressional Black Caucus Chairman Elijah Cummings and the district he represents in majority-black Baltimore.

Last week, NABJ blasted Trump over his Twitter tirade against Baltimore, during which he called the city a “disgusting rat and rodent-infested city.” In a statement, the association said a president who engages in “untruths” and “verbal assaults” in fact “dishonors our country, its citizens and even the legacy of White House.”

Booker on Thursday warned the audience that Trump has endangered their lives by calling the press “the enemy of the people.” And he called on journalists in the crowd to stop asking whether people are racist and start asking whether people are doing anything to address an obvious problem.

“We all have a responsibility and yes, you have a responsibility,” he said. “What are we doing to address the legacy of white supremacy and the way it’s manifested itself so profoundly in our society?”

According to moderator Vann Newkirk, a political reporter for The Atlantic, NABJ invited the top six polling Democrats to participate in Thursday’s forum. The association also invited Trump and former New Mexico Gov. Bill Weld, who is running a Hail Mary primary campaign against the president and was the fourth participant in Thursday’s event.

Sanders, of Vermont, called Trump a demagogue Thursday. But he spent most his half-hour on stage talking about his platform and explaining how his proposals to overhaul the nation’s healthcare system, raise the minimum wage to $15 an hour and alter policing in minority communities will directly benefit African Americans.

“Today we are living in a country in which, as all of you know, white families own 10 times more wealth than black families. Eighty-seven million Americans uninsured or under-insured. The situation is far worse in the African-American community,” he said. “We have maternal deaths three times higher than white women, when infant mortality is 2.5 times higher.”

But much of the forum focused on race, racism, and the country’s ability to overcome a systemic problem that has become a central issue in the campaign for president.

“The longer we allow this to go on,” said Buttigieg, referring to racial inequities in the country’s laws and institutions, “the more likely it is to destabilize the entire country.”

Miami Herald reporter Maya Lora contributed to this report.