As the world ponders the meaning of U.S. President Donald Trump's threat of "fire and fury" on North Korea, it's worth asking why his predecessors never took those steps to stop its nuclear program.

When President Bill Clinton was confronted with the threat of North Korea's exit from the Nuclear Non-Proliferation Treaty, he considered military force. But he ended up going for negotiations in what became known as the Joint Framework Agreement. The North Koreans froze their plutonium program in exchange for fuel shipments and a light water reactor from the United States. Neither side ever fully delivered.

Then there was President George W. Bush. He didn't like North Korea. He put the nation in the original "axis of evil." On his watch, the U.S. discovered Pyongyang had a secret uranium enrichment program, in violation of the spirit of Clinton's deal. Then in 2006, North Korea tested its first nuclear device. By 2007, Bush had lifted crippling sanctions on the regime's elites and entered into new negotiations. And surprise, the North Koreans backed out of those talks at the end too.