A recent satellite photograph of steam rising from a nuclear reactor in North Korea confirms that it has resumed making plutonium that can be harvested and turned into nuclear weapons material. In doing so the rogue nation has violated a pledge made only 20 months ago. It reinforces the grim reality that any hope of progress on the North Korean front is simply illusory.

On similar occasions in 1994 and 2006 Presidents Bill Clinton and George W. Bush talked tough, but their diplomatic initiatives gave North Korea room to move ahead with its program to acquire a nuclear arsenal and long-range missiles to deliver them.

President Clinton did not use the term “red line” in public when he warned North Korea not to process plutonium taken from a non-military nuclear power reactor. But his former defense secretary, William Perry, said in a June interview with Foreign Policy magazine that the president had “drawn a very public and very explicit red line, that they would not process plutonium or that we would take some action.”

Mr. Perry said the most likely response would have been a cruise missile strike on the North Korean plutonium reprocessing plant.

Mr. Clinton was rescued from his threats in 1994 by former President Jimmy Carter, whom he asked to go to North Korea and find a way out of the nuclear impasse.

The result was an agreement that North Korea would not reprocess plutonium taken from the Yongbyon nuclear reactor, and allow it to be monitored by the U.N., if the United States and other nations would supply it with oil and two modern light-water nuclear power reactors that did not produce plutonium as a by-product.

But North Korea secretly began enriching uranium for weapons fuel by a process that has been described as more sophisticated than that used by Iran. When this was exposed in 2002, the United States said North Korea had not lived up to the terms of the 1994 agreement, the Stalinist regime announced that the agreement was dead and began reprocessing the plutonium removed from the reactor in 1994.

In 2006, President Bush issued a warning of his own, telling North Korea not to test an intercontinental missile. “It’s best for all of us to go to the U.N. Security Council and say loud and clear, here are some red lines,” he said.

Meanwhile, William Perry and another Clinton-era defense official, Ashton Carter, wrote an article calling on Mr. Bush to destroy North Korea’s missile before it could be launched, and its missile testing facilities, in order to close the door to North Korea acquiring a missile system that would threaten the U.S.

No action was taken. Last year North Korea launched a missile with the potential to reach the Hawaiian Islands or Europe. And according to a consensus of experts, North Korea already has up to eight nuclear warheads.

Ashton Carter is presently President Obama’s deputy defense secretary.

The military options of 1994 and 2006 remain. But there are difficulties regarding any military action particular to North Korea — primarily its massive standing army and the proximity of the South Korean capital of Seoul to the demilaritized zone.

Odds are that, like his predecessors, President Obama will eschew military options and rely on diplomacy and the carrot of financial aid to solve the latest North Korea crisis. Odds are that he will be just as unsuccessful.

Meanwhile, North Korean is expected to have enough plutonium in about three years to build more nuclear weapons. In many ways, that represents a more direct threat to America than Syria’s brutal regime. And North Korea may eventually provide a more bitterly convincing lesson of what can happen when “red lines” are not enforced.