Walker wants to make clear that he is the most irresponsible hawk on Iran:

Speaking to reporters here Saturday after an appearance at the Family Leader Summit, Walker said the next president will need to be prepared to take aggressive action against Iran, “very possibly” including military strikes, on the day he or she is inaugurated, and said he would not be comfortable with a commander in chief who is unwilling to act aggressively on day one of a new presidency [bold mine-DL].

Walker may think that he is getting the upper hand in the primaries by positioning himself as the most aggressive hard-liner, but in the process he is revealing that he has extraordinarily bad judgment on these issues and confirming that his lack of foreign policy experience is a major liability for him. Why should voters trust him with the presidency when he is eager to boast about his readiness to start an illegal war against a country that just negotiated an agreement with the U.S. and its allies?

The more important thing here is to understand that a preventive war against Iran would be entirely unjustifiable, unnecessary, and illegal under international law. The U.S. would not be defending itself or anyone else by launching an attack on Iran, but it would be committing an outrageous breach of the U.N. Charter. In the process, it would also be exposing its forces and Iran’s neighbors to retaliation and it would risk dragging the rest of the region into a larger war. Michael Lind makes the case that the U.S. should repudiate preventive war once and for all:

The preventive war against Iraq was the stupidest blunder in the history of U.S. foreign policy. That some Americans today, only twelve years later, can even consider the possibility of repeating that blunder in the case of Iran is as remarkable as it is appalling. International law distinguishes between preemptive war, which is legal, and preventive war, which is not.

There is no difference in practice between a war that is called “preventive” and what a previous generation condemned as a war of aggression. Both are unprovoked attacks against another state, and neither can be justified as self-defense without emptying the concept of all meaning. That is what Walker thinks the next president should “very possibly” do as soon as he is sworn in.

Even if Iran were building a nuclear weapon, the U.S. would be in the wrong to launch a “preventive” attack on them. To do so after Iran had started scaling back and limiting its nuclear program would be an even greater crime. Walker’s talk about “very possibly” attacking Iran immediately after taking office would be indefensible warmongering even if there were no deal with Iran. To propose such an appalling idea now that a deal has been reached shows that Walker is so reckless that he should never be trusted with the power of the presidency.