Bill Gates has been warning government leaders about a global pandemic for years, but the coronavirus still caught nations off guard — and the philanthropist and Microsoft co-founder said that’s one of his biggest regrets.

“I wish I had done more to call attention to the danger,” Gates told the Wall Street Journal. “I feel terrible. The whole point of talking about it was that we could take action and minimize the damage.”

Gates began warning about the threat of pandemic disease in 2014. At the time, Ebola was on his radar.

The next year, he gave a TED talk, calling infectious disease a bigger threat to the world than nuclear war and wrote in the New England Journal of Medicine that “an epidemic is one of the few catastrophes that could set the world back drastically in the next few decades.”

It was a theme he tried to impress upon world leaders he met with, including then-President-elect Donald Trump in 2016. But convincing politicians to spend vast amounts of money on something that wasn’t an immediate threat proved a difficult task, according to Gates.

He told the Wall Street Journal that he regrets not pushing harder.

“I wish the warnings that I and other people gave had led to more coordinated global action,” he said. “My hope now is that leaders around the world, who are responsible for protecting their citizens, will take what has been learned from this tragedy and invest in systems to prevent future outbreaks.”

The Gates Foundation has committed $305 million to fight coronavirus so far — and Gates says he expects to invest much more before the pandemic is over.

Gates’ firm stand on coronavirus and safety measures has made him a target of conspiracy theorists. And his foundation’s close ties with the World Health Organization made him a fierce critic of Trump’s recent decision to stop funding the WHO.

He has advocated mass shutdowns to stop the spread of the disease and predicted in early April that life could begin to return to some semblance of normal in June.

Two-and-a-half weeks later, however, that optimism faded, with Gates saying he was “super worried” about a second wave of COVID-19 hitting the U.S. as states began to relax social distancing rules and reopening retail stores.