We may now have the tools to end AIDS. All that's needed is the will.

To leave a longstanding mark in history, President Donald Trump needs more than low unemployment numbers and a string of scandals. He needs a moonshot.

Other leaders have labelled their goals "moonshots," but to be remembered alongside the original moonshot, a big challenge needs a known solution. In the mid-20th century, the science was already in place to build long-distance rockets. Getting to the moon was an engineering challenge.

"Cure cancer" is a popular promise, but no one knows how. But now, for the first time, doctors do have a possible path to eradicating HIV/AIDS.

In the past it was assumed that the world would be stuck with millions of cases of HIV until someone invented a safe and effective vaccine. There isn't one yet. But researchers are publicly speculating that a concentrated effort could end HIV transmission in the U.S., and possibly worldwide, using drugs that already exist.

It's not a sure thing. Even if it works, it won't happen overnight. But neither did Kennedy's moonshot.

There are two reasons for the scientists' optimism. The first is that the antiretroviral drugs now given to people who test positive for HIV also cut their risk of transmitting the virus to others. The other is that a new class of preventive drugs, known as PrEP for "pre-exposure prophylaxis," have shown great success in cutting the risk of acquiring the virus.

The original PrEP drug, Truvada, made by Gilead Pharmaceuticals, was propelled into the headlines last week after the Lancet HIV published results of the first successful large-scale trial. Researchers gave the drug to 3,700 gay and bisexual men in Australia who were HIV negative and were considered at elevated risk for contracting the virus. Only two were infected after a year, and both reported failing to take the daily pill as directed. Of those who took the drug as directed, nobody tested positive after a year.

A daily pill presents a compliance problem that wouldn't have come up with one- or two-shot vaccine, but it's possible that those who are diligent will get protection comparable to the best hopes of vaccine researchers. The successful trial led experts to speculate a two-pronged approach that could finally stop the virus from spreading: ensure that most people with HIV get on antiretrovirals, and ensure that the bulk of HIV-negative people at elevated risk get access to PrEP.

There's a certain amount of cultural baggage that's come along with PrEP. One journalist chronicled his own experience with the drug, excerpted in The Guardian. He advertised his use of PrEP on dating websites (geared at meeting other men) and encountered skepticism and harsh judgment, as people assumed he wanted to avoid using condoms and would put everyone at risk of other infections. A similar moral hazard argument came up in opposition to the introduction of a vaccine that protects against the cancer-causing strains of HPV. Some thought it would encourage promiscuity and condom-free sex.

Setting aside whether promiscuity and condom-free sex should be discouraged - a whole other controversy! - experts point out that even without being on PrEP, people are already having sex without condoms. In parts of Africa where the epidemic is still raging, many men refuse to use them. HIV is still spreading, with about 38,000 new diagnoses each year in the U.S. and 1.8 million worldwide.

Truvada is expensive. A recent story in the medical website STAT reported that as of January, a month's supply cost $1,675.00. While generics have been invented, they haven't reached the market because "Gilead struck deals with the manufacturers." The same article reported estimates that only about 8 percent of people in the U.S. who would benefit from PrEP are getting it.

Companies that could distribute generic Truvada might be tempted to do so if they could share in the glory of ending a disease that has killed 35 million people worldwide. And surely a government-led effort could find a creative way to get the right drugs to the people who need them without bankrupting any pharmaceutical giants. If we can send a man to the moon . . .

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Flam is a Bloomberg Opinion columnist. She has written for the Economist, the New York Times, the Washington Post, Psychology Today, Science and other publications. She has a degree in geophysics from the California Institute of Technology.

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