Republican presidential nominee Donald Trump made a wild claim about President Barack Obama at a Wednesday campaign rally in Ft. Lauderdale, Florida.

President Obama, Trump said repeatedly, "is the founder of ISIS." Trump also called Hillary Clinton, who served as Obama's Secretary of State, the "co-founder."

It's possible that Trump simply meant to link the President's foreign policy with the rise of ISIS.

But his words also seem to invoke previous questions Trump has raised about Obama's citizenship over the years.

Trump's assertion may have not only meant to criticize Obama's handling of conflicts in the Middle East but also to issue a kind of racist dog-whistle — hinting back to his history of suggesting that President Obama was not born in the United States and is a Muslim. To this point, he also lingered on President Obama's middle name, "Hussein."

An NBC News/SurveyMonkey poll of over 1,700 registered voters conducted in June and July found that 72 percent of registered Republicans doubted Obama's citizenship.

From NBC News:

"While more than eight in 10 Democrats agreed with the claim, far more Republicans disagreed with the statement (41 percent) than agreed with it (27 percent). An additional 31 percent of Republicans expressed some doubts about whether Obama is a native U.S. citizen (i.e. indicating that they neither agreed nor disagreed with the statement). Only slightly more than one in four Republican voters agreed that the president was born in the United States."

Trump has been fixated with this pseudo-issue since long before his own candidacy.

He has used his Twitter to call for the release of Obama's birth certificate countless times, though he hasn't voiced these controversial questions so openly during his presidential bid.

Trump's birtherism set the tone for own political rhetoric and candidacy.

Its echoes can be detected in the xenophobic immigration policies he has championed since announcing his run for president: his ban on Muslim immigration, his remarks about Mexican "rapists," and the calls to "build a wall" that seem fill the room at each of his campaign rallies.

"Birtherism was the crucible and the template for Trump’s Presidential campaign," the New Yorker observed. "It foreshadowed so many of its hallmarks: dog-whistle racism, the brazen spreading of thoroughly disproven allegations, the just sayin’ tone in which Trump smears people."

Recently, former Trump campaign manager-turned-CNN contributor Corey Lewandowski revived the birth certificate question on a CNN panel. He was quickly shut down by fellow panelist Angela Rye, who forced him to sheepishly admit that the President was born in Hawaii. "Boy bye," an exasperated Rye exclaimed.