President Trump at a rally in Cincinnati on Thursday pledged that America will "very shortly" find a cure for childhood cancer and end the AIDS epidemic.

"I see what they are doing. I see it. They show me. The things we are doing in our country today. There's never been anything like it," said Trump to cheering supporters.

The rally was held the day after the Democratic debates in Detroit, and also featured the president attacking his prospective 2020 rivals.

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President Trump returned to one of his wilder promises at his rally in Cincinnati on Thursday, saying that under his leadership the US will "very shortly" find a cure for childhood cancer and end AIDS.

"We will achieve new breakthroughs in science and medicine," the president told the cheering crowd Thursday night as he ran through the achievements of his administration.

"I see what they are doing. I see it. They show me. The things we are doing in our country today. There's never been anything like it. We will be ending the AIDS epidemic shortly in America, and curing childhood cancer very shortly."

Trump's boast was similar to one he made at a rally in Orlando, Florida, in June. At that rally he claimed "we will come up with the cures to many, many problems, to many, many diseases — including cancer" and would "eradicate AIDS in America."

At both rallies he pledged that America would soon put a man on Mars.

In his February State of the Union address, Trump pledged that the US would eradicate AIDS within ten years. His administration's 2020 budget proposal requests $291 million to combat the disease.

In the address, he also committed $50 million to pediatric cancer research, in a budget that would see the National Cancer Institute's overall budget slashed by $900 million.

Congress has previously balked at requests to slash federal cancer research funding.

Cincinnati is one of the jurisdictions targeted by the administration's ambitious AIDS plan. Public health officials met with the director of the Centers for Disease Control and Prevention ahead of Trump's rally to discuss their efforts to combat AIDS.

Advocacy groups have criticised Trump's AIDS policies, under which $1 billion was removed from global AIDS initiatives, protections for patients with the disease rolled back, and health benefits for LGBT Americans ended, according to Politico.

Trump was speaking the day after the Democratic presidential debate in Detroit, and spent much of the one-and-a-half hour speech attacking his prospective rivals in the 2020 election, and ad libbing on favorite gripes, including wind energy.

He said: "The previous administration, they like wind mills. If a windmill is within two miles of your house, your house is practically worthless. They make noise, they are intermittent."

"They kill your birds. They break down. You have to replace them every 10 years because they wear out. And they cost a fortune and they need subsidy."