Sioux City, Iowa - Over the weekend, Donald Trump held a rally to win over Iowa voters, where he made a major flub that has some raising questions about his cognitive health.

Several times during his speech on Saturday evening, Trump mistakenly referred to Sioux City as Sioux Falls, a city in South Dakota.

"Very big hello to a place where we've done very well," he told the crowd at one point. "Sioux Falls, thank you very much, Sioux Falls. And thank you."

The former president repeated the mistake so many times that Republican state senator Bradley Zaun, who earlier told the crowd that Trump "is the best president of my lifetime," jumped on the stage to correct him.

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Trump is seen responding "oh" before picking up where he left off.

"So, Sioux City, let me ask you," he went on to say, "how many people come from Sioux City, how many people?... Who doesn't come from Sioux City? Where the hell do you come from?"

The incident has become one of many examples of Trump making public mistakes that are being used to advance concerns about his mental health, a criticism regularly leveled at President Joe Biden.

Trump has noticably steered away from the subject of Biden's age. When asked about it in a recent interview, he stated, "Biden's not too old, but I think he's incompetent, and that's a bigger problem."