John Judis stresses that an attack on Iran would be a preventive war:

Duss and Korb point out–and it’s worth putting in capital letters–that the invasion of Iraq was not a PRE-EMPTIVE but a PREVENTIVE war, as would be aerial attacks against Iran. Iraq was not threatening to go to war against the U.S., nor is Iran threatening to go war against the United States. And preventive wars have never been sanctioned under any international agreement. Anyone but the perpetrator calls them international acts of agression.

This confusion of terminology has been with us at least since 2002 when Bush described a preventive war policy as “pre-emption.” Because pre-emption has some connection to self-defense, however tenuous and strained, it has been more useful for its advocates to describe an unprovoked invasion or attack this way than to call it what it is. To speak of “pre-emption” assumes that there is an imminent threat, but the arguments for the invasion of Iraq and for attacking Iran always referred to a possible future threat that might one day emerge. Pre-emptive warfare is still extremely difficult to justify and the burden of proof would still be on the side that initiates hostilities that it had just cause to use force, but nothing justifies preventive war.

Judis later refers to “people who don’t know the difference between a preventive war and a pre-emptive war,” which lets advocates of preventive war against Iran off a little too easily. This isn’t simply a matter of misunderstanding these concepts. It’s not the case that preventive war advocates don’t know the difference between the two. I am guessing that they understand the differences but expect their audience not to know them. To that end, they deliberately blur the differences and conflate the two concepts to make military action against Iran seem more palatable. If that seems too cynical or uncharitable, don’t forget that this is exactly what Iraq war hawks were doing in 2002-03.