Donald Trump Jr. at a rally Tuesday night mocked former Vice President Joe Biden over his recent pledge to cure cancer if he's elected president.

Trump Jr.'s comments came during his father's kickoff rally in Orlando, Florida, on Tuesday night.

Not long after Trump Jr. went after the former vice president, who's the front-runner for the 2020 Democratic nomination, President Donald Trump took the stage and also promised to cure cancer.

The former vice president lost his son Beau Biden to brain cancer.

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Donald Trump Jr. at a rally in Florida Tuesday night mocked former Vice President Joe Biden over his recent pledge to cure cancer, not long before President Donald Trump took the stage at the rally and promised to do the same.

"What was the good one last week?" Trump Jr. said at his father's 2020 kickoff rally in Orlando, Florida. "Remember? Joe Biden comes out, 'Well, if you elect me president, I'm going to cure cancer.' Wow, why the hell didn't you do that over the last 50 years, Joe?"

Later in the night, the president said his administration is getting closer to curing cancer and other diseases.

"We will push onward with new medical frontiers," Trump said. "We will come up with the cures to many, many problems, to many, many diseases — including cancer and others, and we're getting closer all the time."

"We will eradicate AIDS in America once and for all, and we're very close. We will lay the foundation for landing American astronauts on the surface of Mars," Trump also said.

At a campaign stop in Iowa last week, Biden spoke about losing his 46-year-old son, Beau Biden, to cancer as he pledged to cure the disease if elected president.

"A lot of you understand what loss is and when loss occurs, you know that people come up to you and tell you, 'I understand' if you lose a husband, a wife, a son, a daughter, a family member," Biden said at the event. "That's why I've worked so hard in my career to make sure that — I promise you if I'm elected president, you're going to see the single most important thing that changes America, we're going to cure cancer."

Read more: Trump raised over $1 million per hour on the day of his re-election campaign kickoff, blowing Democrats' fundraising out of the water

Thousands attended Trump's Tuesday rally as the Republican National Committee announced the president's reelection campaign had raised nearly $25 million in less than 24 hours.

Comparatively, Biden, the front-runner for the 2020 Democratic nomination, raised approximately $6.3 million on the first day of his campaign.

Trump might have a low approval rating, but his 2020 campaign has gotten off to a strong start.