The Trump campaign has seized on Joe Biden's gaffe claiming that African-American voters "ain't black" if they consider supporting Donald Trump in November.
Republican strategists have earmarked $1m (€920,000) for an advertising campaign aimed at weakening the former vice-president's support among African-American voters.
The advert highlights Mr Biden's support for the 1994 crime bill, which led to mass incarceration, destroying "millions of black lives".
Tim Scott, a black Republican senator for South Carolina, has launched a website highlighting the comments and is selling #YouAintBlack T-shirts.
Mr Biden has frantically tried to undo the damage, admitting that he was "much too cavalier" in his remarks. "I know that the comments have come off like I was taking the African-American vote for granted. But nothing could be further from the truth. I've never ever done that and I've earned it every time I've run," he said.
The black vote was crucial in rescuing Mr Biden's primary campaign, catapulting him to the nomination. It could also prove pivotal in swing states in the presidential election.
Opinions differed on the damage the remarks would cause. "He has just blown his campaign," said Oliver McGee, an African-American who served in the Clinton administration but has since become a Trump supporter.
Christopher Galdieri, a political analyst at Saint Anselm College in New Hampshire, said he believed the row would die down. (© Daily Telegraph, London)