Donald Trump Jr. harshly mocked John Fetterman's stroke, escalating GOP attacks on his health in the tight PA Senate race

• Democrat John Fetterman and Republican Mehmet Oz are facing off for US Senate in Pennsylvania.
• Fetterman's health has become a focal point of the race after he suffered a stroke in May.

Donald Trump Jr. mocked senate candidate John Fetterman over his stroke, saying he doesn't have "a working brain," deepening Republican attacks on Fetterman's health in a tight race.

The eldest son of former President Donald Trump made the comments at his father's "Save America" rally in Miami, Florida, on Sunday night in the lead-up to the mid-term elections.

"I believe that if you're going to be in the United States senator, you should have basic cognitive function," he told the crowd. "It doesn't seem that unreasonable — to have a working brain."

"We're up against a Democrat party today that doesn't believe that a United States senator should not have mush for brain."

Trump's attack was one of the most aggressive and demeaning in a campaign where Fetterman's health has proved a major issue.

A spokesperson for Fetterman did not immediately respond to Insider's request for comment.

Fetterman, currently the lieutenant governor of Pennsylvania, is running against Republican rival and celebrity doctor Mehmet Oz. You can read Insider's full preview of their race here.

He suffered a stroke in May and developed an auditory-processing disorder. A physician's note he released last month said that Fetterman was recovering well and could carry out public office.

In a heated debate with Oz last month, Fetterman struggled with some of his sentences, which he then acknowledged, telling the crowd: "Let's also talk about the elephant in the room: I had a stroke."

"He'll never let me forget that," he added of his opponent.

Fetterman's health has been a major focal point during the race and many GOP figures, including Republican National Committee Chairwoman Ronna McDaniel, have mocked him for it.

The Oz campaign has also repeatedly questioned Fetterman's ability to serve and insisted he provides a regular update on his health.

"If John Fetterman had ever eaten a vegetable in his life, then maybe he wouldn't have had a major stroke and wouldn't be in the position of having to lie about it constantly," a senior communications advisor to Oz's campaign said earlier this year, to wide condemnation.

Oz has been closing in on Fetterman in recent weeks, according to polls aggregated by the data website FiveThirtyEight, with a negligible difference between the two.

Pennsylvania is a swing state that backed Trump in the 2016 presidential election before flipping to support Biden by 1.2 points in the 2020 election.