Unthinkable: Iran, the Bomb and American Strategy. By Kenneth Pollack. Simon & Schuster; 536 pages; $30. Buy from Amazon.com

RIGHT now the world is gripped by Barack Obama’s efforts to enforce a ban on the use of chemical weapons by Bashar Assad. But the president’s red line in Syria is a faint scribble compared with America’s refusal to contemplate a nuclear weapon in Iran. Time and again Mr Obama has made it clear that, rather than accept an Iranian bomb, he would go to war. The Senate, torn over Syria, voted 90-1 last year against living with a nuclear Iran. Yet such “containment” is just what an engrossing new book by Kenneth Pollack proposes.

The advice offered in “Unthinkable” is all the more striking because Mr Pollack, a former CIA analyst now at the Brookings Institution, was a strenuous backer of the invasion of Iraq in 2003. Mr Pollack is at pains to prove that he has not gone soft, and that he is alive to the dangers of a Shia bomb. His book is needed, he argues, precisely because containment is so scorned in Washington that nobody is properly weighing up the arguments for and against it. That is true, but it is unlikely to redeem him among his fellow hawks.

Mr Pollack thinks that containing Iran is the least bad of several bad options. Chapter by methodical chapter he sets out his case. The evidence is strong that Iran’s nuclear programme is not about civilian power, as it claims, but about weapons. Why, otherwise, would the country expend vast diplomatic and financial resources on enriching uranium in bomb-hardened facilities? A civilian project would buy the fuel on the world market and spend the money on building power stations instead.

A nuclear Iran would pose a grave threat. Saudi Arabia and the other Gulf states could feel obliged to acquire weapons of their own. A many-sided nuclear stand-off would make the two-handed games of the cold war seem almost simple. Like Pakistan, which felt that the bomb equipped it to challenge India, Iran might well throw even more of its weight around the Middle East. Israel, especially, feels vulnerable to the mullahs’ machinations.

Many people conclude that only the threat of military action can hold Iran back, and that despite the costs and the risks, an attack, they say, would be better than allowing Iran to arm itself. Mr Pollack disagrees. His worst outcome would be a solo Israeli raid. Israeli bombers have neither the range, nor refuelling capacity, nor ordnance to mount large, sustained raids on Iran’s nuclear facilities. An attack would cause turmoil in the Middle East and probably set Iran back by only a year or two; it might fail even to penetrate the enrichment plant deep inside a mountain at Fordow, near the holy city of Qom.

An American air strike would certainly be more destructive. But, in the medium term, it might not be all that much more effective. Although it would wreck lots of machinery, Iranian know-how would survive. Iran would probably quit the Non- Proliferation Treaty, stopping international inspectors from monitoring its subsequent pursuit of a weapon. Mr Pollack argues that evidence of Iran’s continued defiance would present America with a horrible choice: defeat over a vital national interest, or an impossibly daunting invasion and occupation that would tie up virtually the entire active-duty American army and marine corps.

Compared with that, Mr Pollack argues, containment has real merits. It need not result in appeasement any more than containing the Soviet Union did. It would rely on American deterrence to stop an Iranian nuclear attack and hard-nosed retaliation to limit Iranian bullying. Vigilant diplomacy would be needed to prevent crises escalating and to ensure that sanctions remained in place. Just as in the cold war, America could campaign for regime change and against the Iranian abuse of human rights.

Unthinkable, and very sensible

Hawks will say that Mr Pollack underestimates the probability of a nuclear attack on Israel—if not by this lot, then by their successors in Iran. Even a remote chance of being bombed would be hard to tolerate for an embattled country that is just 15km (9 miles) across at its narrowest point. Hawks will also complain that “Unthinkable” overestimates the likelihood of American troops being sucked into a full-scale invasion.

Doves, on the other hand, will contend that Mr Pollack is too pessimistic about the scope for negotiating with Iran—especially with Hassan Rohani, the newly elected president and a possible reformer. They will also point out that promoting regime change will only convince Iran that it needs nuclear weapons to remain safe, just like the Kims have been safe in nuclear North Korea, and unlike Libya’s Muammar Qaddafi, who abandoned his programme.

None of that would surprise Mr Pollack, who acknowledges that containment is “not tough enough for conservatives and not compassionate enough for liberals”. That rhetorical flourish is designed to make “Unthinkable” sound, in contrast to its title, reasonable and level-headed. And, to his great credit, Mr Pollack has produced an account that is mercifully free of swagger. If Congress gets a vote on going to war with Iran, let’s hope that this book is on everyone’s reading lists. It might just change a few minds.