Billionaire investor Warren Buffett told CNBC on Monday he would judge President Donald Trump after four years first and foremost by how safe the United States is.

Buffett said on “Squawk Box” his top concern is how to prevent rogue nations from getting weapons of mass destruction, and he singled out North Korea as a specific threat.

The health of the economy at the end of four years is also a yardstick by which Buffett said he’d evaluate the Republican Trump administration.

The chairman and CEO of Berkshire Hathaway, who supported Democrat Hillary Clinton, said he would have judged her by the same standards.

Buffett said there has never been a president thus far that would prevent him from investing in the stock market.