Go figure — most of us thought that sending $1.7 billion to the world’s biggest state sponsor of terrorism was the “height of folly.” Or, perhaps, paying ransom for American hostages in the belief that it would be a one-time demand for Danegeld was the “height of folly.” Instead, outgoing CIA Director warns Donald Trump via a BBC interview not to fulfill his campaign pledge to tear up the deal that produced these humiliations … and he may have a point:

He also warned Donald Trump’s incoming team over their position taken during the campaign to abandon the nuclear deal with Iran.

“I think it would be disastrous,” Mr Brennan told the BBC. “First of all, for one administration to tear up an agreement that a previous administration made would be unprecedented.”

He said such a move would risk strengthening hardliners in Iran and risk other states pursuing nuclear programmes in response to a renewed Iranian effort. “I think it would be the height of folly if the next administration were to tear up that agreement,” he said.

Brennan states that having one administration tear up agreements reached by preceding administrations would set a very bad precedent and cause damage to American credibility. That’s true, but it’s also why the US Constitution has a process for such international compacts: ratification. That makes treaties legally binding in the US, making it much more difficult for succeeding administrations to reverse course. That process requires the executive branch to take more care in entering into agreements in the first place so that they reflect a broad consensus within the US. It’s a key part of the checks against the creation of imperial presidencies, and Obama has gone farther than any of his predecessors in evading that check, and he made sure this agreement didn’t get any input from the Senate.

Brennan’s other substantive objection doesn’t stand up to scrutiny, either. He claims that backing out of the agreement will push Iran into developing nuclear weapons, and that other states in the region will follow suit. That would only be true if (a) the agreement prevented Iran from becoming a nuclear-weapons power, and (b) everyone trusted Iran to stick to the agreement. The agreement only keeps Iran under wraps for a decade or so, at which point Tehran can do whatever it likes. It’s not going to take long for an arms race to begin at that point, and it’s almost a certainty that Saudi Arabia will take steps to protect itself long before then.

Nevertheless, Brennan may be right, but not for the reasons he lays out here. Obama’s surrender on the Iranian nuclear program means that we won’t have the credibility to put the Western band back together to reimpose an effective sanctions regime, former Defense Secretary Robert Gates tells CBS News this morning. Instead, Trump could try forcing a renegotiation — and a tougher approach to Iran than the current administration has taken:

“I think it would be a mistake to tear up the agreement at this point. I think we would be the ones isolated, not the Iranians because none of our partners that helped negotiate that would walk away from it,” Gates said.

“But what I do think the next president can do is push back against the Iranians in all of the other activities — in their behavior in the region and you know, pointing guns at our helicopters and challenging our ships and their meddling in Yemen, their meddling in Syria and having significant troops. We should’ve from the very beginning made it clear that we — we’re not going to allow that the agreement on nuclear materials was not going to inhibit us in the slightest from protecting our friends and our interests in that region against the Iranians,” said Gates.

That’s the state of things on Iran at this point. We have already coughed up the money, so that leverage has dissipated. Obama has also rejected the sanctions regime that at least put some economic pressure on the mullahs to stop their progress toward missile-mounted nuclear weapons, and made it politically impossible for our allies to demand a return to it. The best we can manage at this point is to make those allies nervous enough about Trump’s intentions to wring a few more concessions out of the agreement, but there is no good way to return to the status quo ante.