In a New York Times survey of the foreign policy views of the Democratic presidential candidates published on February 7 (They Reject Trump's Foreign Policy, and Don't Agree on One of Their Own), Bernie Sanders gave answers that generally did not disappoint supporters looking for a major foreign policy shift. There was one exception, however the question "Would you consider military force to pre-empt an Iranian or North Korean nuclear or missile test?" Of the ten remaining candidates who responded to the questionnaire (two had dropped out and two did not reply), Amy Klobuchar skipped the question, Tom Steyer replied without saying yes or no, and six said yes: Michael Bennet, Joe Biden, Michael Bloomberg, Pete Buttigieg, Deval Patrick and Bernie Sanders. The only two no's were Elizabeth Warren and Andrew Yang.
There is no particular reason to think that this answer portends a Sanders retreat from a foreign policy profile that has generally seemed an across the board improvement from 2016, when Sanders seemed to have grown rusty on that front over the years spent concentrating on domestic economic issues. The very next night, for instance, in response to a New Hampshire debate question about the assassination of Iranian General Qasem Soleimani, he went deeper in his foreign policy critique than the rest of the Democratic field in saying, "What we have got to do is bring countries around the world together with our power and our wealth and say, you know what, let us sit down and work out our differences through debate and discussion at the UN, not through more and more war and the expenditures of trillions of dollars and the loss of God knows how many lives."
Nonetheless, his mistake on the Iran/North Korea testing question is too important for even his partisans to ignore. Indeed the fact that even a Bernie Sanders could think that it is within our rights to launch an attack on another country, not because that country has attacked us, and not because that country is presumed to be planning an attack upon us, but to preempt the development of a weapon or weapon delivery system that might someday be used against the U.S., is a measure of just how warped this country's sense of its rights and obligations under international law has become.
One clearly relevant fact is that while North Korea was once a party to the Nuclear Non-Proliferation Treaty, it has withdrawn and now is one of the world's five non-member nations, along with South Sudan, India, Pakistan, and Israel, which have never signed. So, much as we might wish that it would not test and develop nuclear weapons, like those countries North Korea is not in violation of any treaty when it decides to do so (as three of the other four have done.)
And then there's the matter of Article VI of the Nuclear Non-Proliferation Treaty, under which, "Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control." This treaty was first signed in 1968, so the called for "early date" for "a treaty on general and complete disarmament" would surely seem to have passed by now. Certainly there's been no noticeable effort on the part of the American government to make it a reality thus far in this millennium.
But even beyond these salient points, there is the more basic one that the U.S. simply has no right to attack either of these countries. Such an attack would fundamentally differ from the Bush Administration's war against Iraq only in degree perhaps, depending on the nature of the attack. A point generally now lost in the discussion about the Iraq War is that it was not justified not because the administration (and Tony Blair's U.K. government) falsely claimed that Iraq had "weapons of mass destruction," but because we invaded a country that had not attacked the U.S., and gave no evidence that it planned to do so.
So this 2016 Bernie Sanders Convention Delegate and 2020 supporter wants to say, "Hats off to Elizabeth Warren and Andrew Yang;" hopes that Sanders won't make this sort of mistake again; and thinks our goal should be that no one outside of the Trump wing of the Republican Party thinks it's okay to threaten the rest of the world in that fashion.