President Trump admits US strike against Iran would have been illegal

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Yesterday President Trump apparently aborted a US strike against Iran, in response to Iran’s destruction of an unmanned US surveillance drone. US and Iranian accounts continue to differ on whether the drone was shot down in Iranian airspace or in international airspace. Ashley Deeks and Scott Anderson have helpfully analyzed the international legal framework applicable to any US strike in response to the destruction of the drone over on Lawfare, to which I have little to add in principle. In particular, they’ve explained the more expansive and the more restrictive theories of self-defence on which the legality of a US strike would hinge (see also Ashley’s previous post here).

But, President Trump has tweeted in the past hour, as he does, and his tweets effectively (if inadvertently) admit the illegality of the aborted US strike under any conceivable theory of self-defence, no matter how expansive:


Note, first, how President Trump describes the aborted US strike as being meant ‘to retaliate’ against Iran for the destruction of the drone. But it is black letter jus ad bellum that the purpose of self-defence can only be to stop an ongoing attack, or (possibly) to prevent imminent future attacks. It cannot, however, simply be to retaliate against an attack committed in the past. Thus, even if US historically expansive views on the right to self-defence were to be accepted in their totality, and even we were to accept that the US drone was in international airspace when it was shot down and that this was an armed attack by Iran against the US in the sense of Article 51 of the UN Charter, the US head of state has just admitted to the world that the strike he authorized, and then rescinded, was retaliatory and not defensive in nature.

Similarly, he expressly admitted that the attack would have been disproportionate, as 150 lives would likely have been lost for one destroyed unmanned drone. And as we all know, proportionality is a key requirement of the customary law of self-defence. Thankfully, President Trump ultimately decided to abort the strikes, and therefore no violation of Article 2(4) of the UN Charter took place. Hopefully any conflict between the US and Iran will be avoided. But that said, it is also clear from what the US President tweeted to all of us, so explicitly and so ungrammatically, that the proposed military action of his government, had it taken place, would have been illegal. And again, under the President’s own admission, it would have been illegal regardless of whether one embraces a more restrictive or a more expansive theory of self-defence.

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Aurel Sari says

June 21, 2019

Is it not too much to assume that the word retaliate was chosen with any degree of legal precision? Asking for a friend.

Marko Milanovic says

June 21, 2019

Why assume anything other than the word's plain meaning? This was after all the person making the decision to strike (or not), and if he says his purpose was to retaliate, then this is what it was.

Aurel Sari says

June 21, 2019

I hear what you are saying, but my friend wonders precisely why we would should not assume that the word was chosen in anything but its plain, non-technical meaning to describe ‘hitting back’, rather than as a more sophisticated expression of a legal rationale. More talk bigly, than talk legally, my friend says. Incidentally, he also wonders whether tweets should be construed with reference to Art 31 VCLT, mutatis mutandis.

Marko Milanovic says

June 21, 2019

Oh, to be clear, I am not suggesting that Trump's statements should be seen as a sophisticated expression of anything, let alone of a legal rationale. They should be seen as an expression of his basic purpose in making his decision to strike or not strike. He is best placed to describe his own state of mind. And he described it as retaliation, not as any kind of defence against an imminent Iranian attack. So that's what it was.

Mary Ellen O'Connell says

June 21, 2019

Dear Marko,

You have chosen the right word--"inadvertently"--when you say Pres. Trump admitted his retaliatory strike would be unlawful. Has he ever show any true interest in the international law on resort to force?

He backed off the strike because he deemed it disproportionate, but that is a second line of analysis. The first is the legal basis for a resort to military force. None exists for such a retaliatory or reprisal attack as I wrote here after the 2018 Syria strikes.

Are we helping to weaken the Article 2(4) by providing nuanced analysis of the potential meaning of words, rather than pointing out the plain fact of illegality?

My impression on hearing that Trump considered the attack potentially disproportionate was that he made an ethical or a business judgement, not a legal one.

The U.S. wants Iran to commit legally to ending its nuclear program. The U.S. should lead, therefore, in robust commitment to the international rule of law.

Mary Ellen

Will Worster says

June 21, 2019

I am also concerned that Trump appears to be saying that the military proposed an operation to him that constituted a disproportionate use of force. He certainly did not prepare the targeting himself.

I don't think I have ever heard the President use the word "proportionality" before, so I can only guess that it was used in the briefing to him.

This could be disproportionate in the sense of jus ad bellum or jus in bello (assuming it constitutes armed conflict, etc.).

My experience so far has always been that the US military was deeply professional and, certainly at these levels of command, would never contemplate conducting a disproportionate use of force. Did they suddenly break with this practice and really propose this to him? And it was only blocked by his better judgment?

Setting aside whether Trump appreciates this or not, he is either lying - and has no hesitation smearing the professional reputation of the Department of Defense - or he is telling the truth - and the US military has indeed abandoned its historic professional approach. You can imagine which one of these possibilities I guess is correct.

Mohammad Rubaiyat Rahman says

June 22, 2019

"... it is black letter jus ad bellum that the purpose of self-defence can only be to stop an ongoing attack, or (possibly) to prevent imminent future attacks. It cannot, however, simply be to retaliate against an attack committed in the past." -

Regarding the ongoing tensions in the Strait of Hormuz, the above mentioned lines of the write up require further commentary as to links between (a) attack committed in the past and (b) purpose of self-defense.

There are reasons why one cannot categorize the shot down of the US unmanned drone as a 'single past incident'.

One is that the incident is stitched with an ongoing crisis in the Gulf of Oman and the Persian Gulf where tankers has been blazed with mines.
The other reason is that the geographical feature of the strait of Hormuz does not always permit Iran to have clear 12 nautical mile territorial sea. The narrowest point of the Strait of Hormuz between Iran and Oman is approximately 21 nautical miles and here, interesting fact is that the drone shot down incident happened in close proximate to those narrow points. What is further more interesting is that both Iran and the USA has not yet ratified the 1982 UNCLOS.

The drone shot down incident revealed that Iran failed to show any restrained attitude where ambiguities regarding territorial sea limit exists. In past, back in mid-1980s, Iran showed similar attitude during tension in the Strait of Hormuz.

Aren't these incidents sufficient enough to assume that in future, there would be no exception in behavior? Isn't it provide a hint of further imminent future attack in the Strait of Hormuz?

Heiko says

June 22, 2019

Well, 21 seamiles, couldnt that part of the strait be a case of collectiv dominium of the two states? And in such a case there may be no protection of possession anyway. As in paragraph 866 of the German BGB: Besitzen mehrere eine Sache gemeinschaftlich, so findet in ihrem Verhältnis zueinander ein Besitzschutz insoweit nicht statt, als es sich um die Grenzen des den einzelnen zustehenden Gebrauchs handelt.

Heiko says

June 22, 2019

Or lets imagive that the two states would agree to close it. Would anybody be allowed to open it again? And could that agreement be an attack on the civilian population in other countries?