Testing nuclear weapons by detonating warheads is like “nuking yourself in the foot,” writes @nuclear-jim.bsky.social. Trump can stop nuclear anarchy by testing in ways that don’t spark a global arms race or give away the U.S.’s data advantage. More here: carnegieendowment.org/emissary/202...

Let's not nuke ourselves in the foot! I explain why it's so difficult to know if China and Russia are conducting ultra-low yield tests and why, even if they are, it's not in U.S. interests to restart testing. @carnegieendowment.org @carnegienpp.bsky.social carnegieendowment.org/emissary/202...

I am entirely indifferent whether, in the event of a nuclear war, I am incinerated by a nuclear warhead delivered by a "traditional" ICBM, a hypersonic glider, a nuclear-powered cruise missile, or a nuclear-powered torpedo. All seem equally suboptimal to me.

¯\_(ツ)_/¯

The End of MAD? Join me, Steve Fetter, @jaysankarans.bsky.social, TD MacDonald, Ton Stefanik, @lauraegrego.bsky.social, @fiona-cunningham.bsky.social, and Charlie Glaser to discuss whether technological developments are undermining mutually assured destruction. Link for virtual rego in next post.

What exactly is the government hiding in Tucson? Not much, says @nuclear-jim.bsky.social. He got an interesting souvenir there, regardless. See the first installment of Carnegie Office Hours for more treasures from James (if not nuclear secrets) here: buff.ly/dlUzF6n

I feel pretty strongly the @nytimes.com has the wrong framing here. This isn't serious; it's pathetic. I'd suggest something like: "Trump throws social media hissy fit invoking nukes after public spat with ex-president of Russia."

As much as I deplore nuclear signaling by tweet--can't believe I just wrote that--I would NOT necessarily assume there's a been change to the US nuclear posture. The U.S. always keeps ~4/5 SSBNs at sea ready to fire.

Ahem (Deleted earlier version, which was missing caption!)

Ah, yes, that crucial ninth significant figure...

Good gracious, Ignatius! Why I disagree with the normally excellent David Ignatius; recent oped on Iran.

The case for attacking Iran relied on emphasizing its technical prowess. The case that strikes were successful requires claiming that Iran is technically incompetent. foreignpolicy.com/2025/07/25/i...

On Friday, I argued in @foreignpolicy.com that Trump admin claims it had set Iran back by "years" were true but disingenuous. The same day, the normally excellent David Ignatius amplified the misleading U.S. and Israeli narrative. www.washingtonpost.com/opinions/202... Let's take a look... (1/n)

🎶When you attend a funeral, It is sad to think that sooner orl… …ater, those you love will do the same for you. And you may have found it tragic, Not to mention other adjec.. …tives to think of all the weeping they will do. 🎶 RIP, Mr Lehrer.

Me in @foreignpolicy.com. The Trump administration's claim that Iran would need "years" to rebuild its previous nuclear program is like asserting that an unlocked bank vault would be impervious to a cyberattack. It’s true but misses the point. foreignpolicy.com/2025/07/25/i...

had @nuclear-jim.bsky.social on Angry Planet to explain what the current nuclear arm's race looks like. It's bad! He's got a solution that sounds radical, but is more palatable than living in a world where everyone is spending billions to construct more nukes

🧵How much damage was done to Iran's nuclear program? An analysis of Friday's reporting of the U.S. government assessment. I'll focus on the @nytimes.com, which was clearer than the earlier but confused @nbcnews.com story. (1/n) www.nytimes.com/2025/07/17/u...

I can think of no reason at all why Iranian leaders won’t jump at the chance to follow the “Libya model.” Can you, Muammar?

Important piece from @nuclear-jim.bsky.social about how to develop a better nuclear deterrence posture. www.cfr.org/report/optim... James’ deep thinking on these matters is desperately needed at a time when deterrence debate at times sounds more like Cold War grab-bag posturing on autopilot.

Personally, I'm open to all three possibilities--that all, some, or none of the HEU was moved pre-war. I simply don't know and there appears to be real disagreement among intel agencies here.

It'd be a pretty catastrophic outcome *IF* the attacks on Fordow failed to destroy centrifuges and they can be put back into service. I'm not claiming this is the case, but U.S. officials seem to be hinting it's a possibility. (1/n) @hugolowell.bsky.social

lol

🧵Introducing optimal deterrence. Here's my proposed U.S. nuclear strategy for managing escalation, arms racing, and proliferation with two nuclear peers, published through @cfr.org. Health warning: If you like counterforce, take a DEEP breath before reading on. (1/n) www.cfr.org/report/optim...

"It always seemed to me that [diplomacy] was a much more promising avenue than military action, which has only modestly eroded Iran’s capability to build the bomb, while increasing its incentives to do so.” @nuclear-jim.bsky.social @newstatesman.com on Iran: www.newstatesman.com/internationa...

My friend, Joshua Pollack, penned this beautiful and wry double obituary of his father, Jonathan Pollack, and his first boss, Barry Blechman. www.armscontrolwonk.com/archive/1220...

This.

The administration has argued that the destruction of Iran's uranium metal production lines at Isfahan will set its nuclear-weapon program back by "years." At Arms Control Wonk, I argue it may not even set Tehran back by months. www.armscontrolwonk.com/archive/1220...

In today's @financialtimes.com, I reflect on the implications of the joint Israeli-US attacks on Iran for a fragile and bruised nonproliferation regime on.ft.com/45Jehd3

Then: We must go to war with Iran to deny it enrichment. Weaponization is too easy to be a useful barrier to proliferation. Now: Meh. It’s not a biggie that Iran has retained its HEU and centrifuge components. Weaponization is a major bottleneck.

Iran has ALREADY dug out the tunnels at Isfahan, where most of Iran's highly enriched uranium was stored prior to attacks and PERHAPS during them. (1/2) www.cnn.com/2025/06/27/p...

In @foreignpolicy.com I wrote about Iran and why nuclear uncertainty is bad for regional stability. Unclear diplomatic priorities + backlash against the IAEA w/in Iran are setting us down a dangerous path. @carnegieendowment.org @carnegienpp.bsky.social foreignpolicy.com/2025/06/27/i...

An analogy. A patient has a tumor behind an abscess. A surgeon operates, skillfully removes the tumor, but predictably ruptures the abscess causing life-threatening sepsis. Afterwards the doctor says, "the abscess wasn't my problem." Do you think the surgery was responsible?

Two days after the recording, I just listened to this, and if I may say so, I don't think I've done a better interview. www.youtube.com/watch?v=VaSA...

There’s lot of disagreement between friendly intel agencies over the location of Iran’s HEU. But even the best case is… not good. www.nytimes.com/2025/06/26/u...

Telling comments from Sens. Cotton and Graham. It's incredible--and not in a good way--to fight war that's nominally for nonproliferation and end up with several bomb's worth of highly enriched uranium (after further enrichment) left unaccounted for.

Come and work with us! We're hiring for a new program assistant. Apply by June 30! carnegieendowment.applicantpro.com/jobs/3780781

If Iran left highly enriched uranium in the Isfahan tunnels, it's not "buried beneath rubble." The U.S. didn't try to collapse them with the GBU-57; they're too deep. The U.S. attacked the tunnel entrances, which won't, in itself, prevent recovery. @barakravid.bsky.social x.com/james_acton3...

James’ entire analysis is worth reading but here’s the bottom line: Iran has the means to build a bomb fairly quickly, it now has a strong incentive to do so, and we probably wouldn’t see them doing it.

How effective were strikes against Iran? U.S. and Israeli officials stress how long it would take Iran to rebuild its previous nuclear program. But there's a MUCH more important issue: How long it would take Iran to get the bomb? For that, a small program would suffice. (1/n)

Here’s the thing about a “low confidence” assessment. While the agency offering it is acknowledging it could be wrong, it’s still saying that its estimate is more likely to be correct than any alternative.

Some thoughts about Trump's comments today re further nuclear diplomacy with Iran + the Majlis bill to suspend Iran's cooperation with the IAEA (tldr: individually: bad, together: very bad!)

A single cascade of 174 IR-6 centrifuges could produce a bomb's worth of 90% highly enriched uranium from the 60% enriched material whose location is unknown in 10-20 days. Iran doesn't need to rebuild enrichment facilities on their previous scale to get the bomb.

Also, we’ll lose continuity of knowledge on Iran’s activities that’ll be difficult to reestablish without a serious forensic effort.

If the centrifuges are still operational, that’s a huge deal. If the issue is whether U.S. strikes collapsed the facility vs. “merely”destroyed centrifuges, it’s not.* What's a HUGE deal is that the U.S. thinks most of Iran’s highly enriched uranium survived. www.timesofisrael.com/liveblog_ent...

This is REALLY bad--and an utterly predictable consequence of military action. Inspectors can't now verify Iran's several bombs worth of highly enriched uranium. This is a MUCH bigger risk than whether the damage done to Fordow meets expectations.

🚀 #SWF launches “Strengthening Strategic Stability at the Nexus of Nuclear & Space Security” with @carnegiecorp.bsky.social + @carnegieendowment.org. Join the Space Boot Camp + Dialogue Series led by @vsamsondc.bsky.social & @nuclear-jim.bsky.social 🔗 swfound.org/space-nuclea...

You’re totally right. Apologies all round. I’ve deleted and will repost linking to a different tweet.

Fact check: True! (Though dirty bombs could be highly, highly disruptive.)

So, the Defense Intelligence Agency is even more pessimistic than me about the effects of the strikes. Last night in @politico.com, I said Iran could get the bomb in a year. Now the @nytimes.com report that implies Iran could have the bomb in ~9 months.