After the September appearance, Bolden said racist messages flooded his voice mail and email.
" 'You n-word, S.O.B.,' " Bolden recounted from one voice mail, censoring the caller's language. " 'You're making millions as a lawyer while I'm making $10 an hour, and you have the audacity to complain about racism in this country.' "
President Trump has said his fight with NFL players is about respecting the flag and honoring veterans — not race. But the president and some conservative commentators have made wealth a part of the debate, inflaming racial resentment among Trump's white working-class supporters who express no tolerance for black athletes raising concerns about institutional racism while making millions of dollars a year.
Players should be "respectful of the national anthem and flag on behalf of the many Americans who have died defending your right to become a millionaire," said Newt Gingrich, a former House speaker and Trump supporter, during an appearance on Fox & Friends several weeks ago.
Joe Walsh, a former GOP congressman and a syndicated radio talk show host who supports Trump, blasted legendary musician Stevie Wonder for kneeling during the anthem at a Sept. 23 concert. "Another ungrateful black multi millionaire," he tweeted.
Tensions over the protests flared anew after ESPN reported last month that Houston Texans owner Bob McNair, who donated $1 million to Trump's presidential inauguration, said, "We can't have the inmates running the prison."
McNair apologized, and most Texans players knelt during the national anthem before their game that Sunday against the Seattle Seahawks.
The argument that professional athletes or high-end lawyers such as Bolden are ingrates suggests they didn't work for their wealth and reflects a sentiment that people of color receive preferential treatment over whites, said Khalil Muhammad, a professor of history, race and public policy at Harvard University's Kennedy School of Government.
A poll conducted this year by The Washington Post and the Kaiser Family Foundation found 28 percent of the general public thinks whites losing out because of preferences for blacks and Hispanics is a bigger national problem than the reverse. That rose to 46 percent among those who strongly approve of Trump's performance.
"The resistance to black advancement is an old problem and repeated pattern in the country, and what whites are reasserting is the privilege of their identity, which translates for many of them into various forms of patriotism and white nationalism," Muhammad said. "The symbolism of black athletes, a representation of black success, kneeling threatens to take that from them."
Trump's attack on the NFL players is a reflection of that belief, some observers say. He first targeted the athletes in late ember, when he said during a Huntsville, Ala., rally, "Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, to say, 'Get that son of a bitch off the field right now, out. He's fired. He's fired!' "
The next day, Trump tweeted if "a player wants the privilege of making millions of dollars in the NFL, or other leagues" they should be made to stand for the national anthem.
The White House declined to comment for this story.
Gingrich continued the theme on Fox News, saying "If you're a multimillionaire who feels oppressed, you need a therapist, not a publicity stunt."
A recent study found higher-income African Americans report more personal experience with racism. Among African Americans earning more than $75,000 a year, 65 percent said someone had used racial slurs to refer to them or other black people, compared to 40 percent of African Americans earning less than $25,000 a year. And 55 percent of high-earning black people said people had acted afraid of them versus 33 percent of lower income African Americans.
The survey, which NPR conducted with the Robert Wood Johnson Foundation and the Harvard T.H. Chan School of Public Health, found that 92 percent of all African Americans say black people are discriminated against, while 55 percent of white Americans say white people are discriminated against.
Trump has struggled to connect with black Americans. He received 8 percent of the black vote in the 2016 general election — the same proportion of blacks who approved of his performance in a Gallup poll in October.
Since taking office, he has engaged in public arguments with African Americans such as Rep. John Lewis (D-Ga.), a civil rights icon who Trump said was "all talk" and "no action."
He withdrew a White House invitation for the National Basketball Association champion Golden State Warriors after star player Stephen Curry said he didn't want to make the customary congratulatory visit.
The president and his press secretary also said ESPN host Jemele Hill should be fired after she said in a tweet Trump was a "white supremacist."
Last month, Trump drew criticism for a feud with two black women — Myeshia Johnson, wife of an Army sergeant killed during an ambush in Niger, and Rep. Frederica S. Wilson (D-Fla.), a friend of the family who said the president's condolence call to the widow was disrespectful and upsetting.
Chuck Creekmur, founder of entertainment news site AllHipHop.com, said it was "absurd" for wealthy men such as Trump and Gingrich to purport to speak for the plight of working-class whites, then argue wealthy black men have no credibility to speak about social injustices in black communities.
"There is no separation between a Stevie Wonder and a Tamir Rice," Creekmur said, referring to the 12-year-old black boy who was playing with a toy gun when he was shot to death by a Cleveland police officer in 2014.
The officer shot the child within seconds of encountering him.
"If you don't feel any pain or anguish about that scenario, I question your humanity. And that's why people are taking a knee," Creekmur said.
Leah Wright-Rigeur, a professor of public policy at Harvard's Kennedy School, also noted the irony in Trump and his supporters criticizing the athletes for making political statements.
"People don't necessarily pay attention to the fact that they say in one breath, 'I don't want to hear what sports people have to say about politics,' but then they will listen to a reality TV star or a rock-and-roll star like Ted Nugent rail against whatever is the political hot topic of the moment," she said. "It's about who is allowed to complain, whose voices are allowed to be heard and who is allowed to discuss America and its institutions."
Trump has tried to reframe the focus on the protests, started last year by former San Francisco 49ers quarterback Colin Kaepernick as a statement about racial injustice, in particular the disproportionate killings of African Americans by law enforcement officers.
In a dramatic response to the player protests, Vice President Pence, at Trump's instruction, walked out of an Indianapolis Colts game Oct. 8 after several players with the visiting San Francisco 49ers knelt during the anthem.
Eric Reid, a safety with the 49ers who has been a vocal supporter of the protests, told reporters afterward Pence's action smacked of "a PR stunt."
Muhammad said the athletes under attack are displaying patriotism by protesting what they see as oppression at the hands of the state, including against some white Americans.
They are "living up to the highest ideals that America claims to stand for, which is to take their power, privilege and prestige and use it on behalf of people who are marginalized, some of whom are white and some of whom also get shot down in cold blood, unarmed in the middle of the street."
Sophia Nelson, a political strategist and author of the book "E Pluribus One: Reclaiming Our Founders' Vision for a United America," said the pressure to silence the protesting athletes is not unlike that faced by African Americans in corporate offices who fear their careers could be jeopardized if they make too much noise about racism or discrimination.
"The president is blowing a very loud dog whistle," said Nelson, who is African American. "He's saying these men don't have rights and if they try to exercise those rights . . . they ought to be fired from their jobs — blackballed."
Indeed, supporters of Kaepernick, who opted out of his contract with the 49ers this year, note he has not been picked up by another team, although quarterbacks with similar or lesser stats and experience have been signed.
Nelson, a member of the GOP for two decades before leaving the party several years ago, criticized prominent Republicans for not speaking up to defend the athletes' First Amendment rights.
Bolden said his critics demonstrate the irrationality of racism — in disputing his contention that racism still exists, even for a successful African American, they pelted him with racial slurs.
Referring to the president's mixed response to the outbreak of deadly violence at a white-nationalist rally in Charlottesville this past summer, Bolden said it doesn't help improve race relations "when Donald Trump can't figure out or equivocates about white supremacy and the KKK and neo-Nazis. It only exacerbates our concerns and our fear as African Americans."