Donald John Trump keeps demonstrating something what many of his fellow Americans have believed since the moment he declared his candidacy for the presidency of the United States.

He doesn’t know — or chooses willfully to ignore — what it means to be leader of the world’s most powerful nation.

He now is taunting the leader of another nuclear-armed nation, telling North Korean dictator Kim Jong Un that the United States has a bigger nuclear button than the North Koreans have. “My button works,” Trump said in a tweet.

Good, ever-lovin’ grief, dude!

Former Vice President Joe Biden, who knows a thing or two about power and its consequences, said “This is not a game … This is not about, ‘Can I puff my chest out bigger than yours.’ It’s just not presidential.”

Trump has drawn intense criticism not just from Democrats, such as Vice President Biden, but from foreign-policy experts. They say Trump’s public boasting about the American nuclear arsenal dismisses decades of presidential protocol.

As Politico reports: “You don’t brandish these weapons. You allude to them, obliquely,” said Joe Cirincione, a former congressional aide and president of the pro-disarmament Ploughshares Fund.

Trump doesn’t have an “oblique” bone in his body. He doesn’t grasp the nature of nuance. He doesn’t understand the consequences of the rhetoric that flies out of his mouth.

He taunts Kim Jong Un as “little Rocket Man” and now declares what the entire world knows already, that the United States can obliterate the entire planet if it so chooses.

This is a dangerous game the president is playing. His itchy Twitter fingers along with his big and boastful pie hole are potentially placing all of his fellow Americans in grave peril.

But … his base keeps insisting: He’s just “telling it like it is.”

Frightening.