Bill Gates is largely 'optimistic' about the future - but a key tenet of the Trump administration worries him

Bill Gates hasn't kept quiet about his thoughts on President Donald Trump and the future of the United States.

In December, Gates told CNBC that "there can be a very upbeat message" about a Trump administration.

But his message hasn't been as optimistic of late.

When asked his thoughts on the current state of the US in a recent Reddit AMA, or "ask me anything," Gates said that though he's positive about the future of the country - especially in the long run - there's one big thing that worries him.

"I am concerned in the short run that the huge benefits of how the US works with other countries may get lost," Gates said. "This includes the aid we give to Africa to help countries there get out of the poverty trap."

Gates has voiced similar sentiments before. In February, USA Today reported that the richest man in the world "expressed concern over the inward-looking nature of nationalist movements." Gates explained to the news outlet that the US government's $30 billion in monetary aid to poor countries is crucial to preventing deaths and helping organizations like the Bill & Melinda Gates Foundation function effectively.

But both Gates and his wife Melinda believe that President Trump's policies might stand in the way of that continued aid.

"If you interpret America First (the stated doctrine of President Trump) in certain ways, it would suggest not prioritizing the stability of Africa and American leadership," Gates told USA Today.