When former President Donald J. Trump questioned Vice President Kamala Harris’s racial identity on Wednesday, he lifted a longstanding and false line of attack from the fringes of political discourse to the very center of a presidential campaign.

For years, rivals and critics have lodged accusations that Ms. Harris shifts her personal identity to her political advantage, and that she is, in fact, not who she claims to be. Those attacks, based on falsehoods, misinformation and conspiratorial notions, have increased dramatically in the week and a half since she emerged as the Democrats’ all-but-certain standard-bearer.

Just hours after President Biden announced that he would not seek a second term, the right-wing agitator Laura Loomer posted on the social media site X that Ms. Harris “pretends to be black” as part of what she called a “delusional, Democrat DEI quota.”

The next day, Tucker Carlson, the former Fox News host who spoke at the Republican National Convention last month, said on his popular interview show that the vice president was “sort of Black, sort of Indian.” The rapper Lil Pump, a Trump supporter who has some 20 million followers across Instagram, TikTok and X, said on Sunday that “Kamala Harris isn’t even black…she’s Indian.”

Their comments, seemingly aimed at suggesting to Black voters that the Democratic candidate does not represent them and, more broadly, planting the idea that Ms. Harris is inauthentic, helped turn what had been a trickle of such content into a gusher. Overnight, conservative corners of the internet, long fixated on Mr. Biden’s age, swung to what looked to be their newest target. Years-old video clips of Ms. Harris acknowledging her South Asian heritage found fresh currency, along with memes mocking her speaking style and even a Billy Joel song modified to say that “she’s not Black or white, Indian, Jamaican.”

In fact, the vice president is the daughter of a Black Jamaican father and an Indian mother, both of whom immigrated to the United States before Ms. Harris was born in Oakland, Calif. She has long identified as both Black and Indian.