Donald Trump is pushing President Barack Obama's buttons.

It wasn’t like Obama needed another reminder of how abruptly his legacy could be upended by a Donald Trump presidency, but the billionaire gave him one this week when he suggested blowing up decades of non-proliferation policy. The Republican front-runner’s musings about letting South Korea and Japan have nuclear weapons and refusing to rule out using nukes in Europe or the Middle East prompted fresh sounds of alarm from Obama.


“The person who made the statements doesn’t know much about foreign policy or nuclear policy or the Korean peninsula or the world generally,” Obama told reporters as he finished the last of a series of high-level meetings on nuclear security in Washington.

Obama has started taking on Trump’s inflammatory comments regularly, condemning his calls to bar Muslims as contrary to American values and warning that the billionaire’s bombast threatens America’s stature in the world. But on the nuclear issue, Trump hit at a topic that is especially close to Obama’s heart.

Nonproliferation was a top focus of Obama’s short career in the Senate, and his pledge to work toward a “world without nuclear weapons” within months of taking office office was a big part of the Nobel Committee’s rationale for giving him the Peace Prize in 2009. Trump’s comments, Obama said on Friday, proved to be a distraction at the 2016 Nuclear Security Summit, the last of four biannual gatherings where, he said, participants have made “significant and meaningful progress” in securing radioactive materials.

“It came up on the sidelines” of the summit, Obama said. “I’ve said before that, you know, people pay attention to American elections. What we do is really important to the rest of the world, and even in those countries that are used to a carnival atmosphere in their own politics want sobriety and clarity when it comes to U.S. elections because they understand the president of the United States needs to know what’s going on around the world.”

Trump has maintained that unpredictability is key to his effectiveness as a negotiator and leader on the world stage, and he’s stuck to that when it comes to the nuclear trigger.

“I’m not going to use nuclear, but I’m not taking any cards off the table,” Trump said when asked repeatedly by MSNBC’s Chris Matthews on Wednesday whether he would rule out using those weapons in Europe or the Middle East.

Trump also caused great alarm in South Korea and Japan, who depend on their alliance with the United States to ward off threats of a North Korean nuclear weapon, when he told Anderson Cooper on Tuesday, “Japan is better if it protects itself against this maniac of North Korea.”

Trump added, "We are better off frankly if South Korea is going to start protecting itself ... they have to protect themselves or they have to pay us."

Obama sought to reassure those countries on Friday.

“Our alliance with Japan and the Republic of Korea is one of the foundations, one of the cornerstones of our presence in the Asia Pacific region,” Obama said. “It has prevented the possibilities of a nuclear escalation and conflict between countries that in the past and throughout history have been engaged in hugely destructive conflicts and controversies. So you don’t mess with that.”

Obama said that through the “sacrifices” of Americans who fought in World War II and the “wisdom” of American foreign policy in the decades since, “We’ve been able to avoid catastrophe in those regions, and we don’t want somebody in the Oval Office who doesn’t recognize how important that is.”

While Obama has rejected Trump with growing urgency, he is staying mum on who should be elected in his place. He’ll certainly endorse the winner of the Democratic primary, but he already got to weigh in as an individual, voting absentee in Illinois’ Democratic primary last month. A reporter asked him which candidate got his vote.

“It’s a secret ballot, isn’t it?” he replied, with a tight smile and a hint of irritation in his voice. “No, I’m not going to tell you now.”

