Part of the lesson people seem to be drawing from the revelation of Peter Costello’s 2005 leadership threats is that they confirm the Treasurer’s lack of backbone: he planned to challenge, but then backed down again. But I’m not convinced that interpretation is right.

It could also be that Costello never intended to carry out the threat.

A challenge and move to the backbench might have meant throwing away his career — but if the threat had worked, none of that would have mattered.

The question of carrying out a threat only comes into play after it has failed in its initial purpose; as I wrote a year ago, “it’s sometimes sensible to make a threat that it would be stupid to carry out.”

Those of Costello’s (and my) generation are unlikely to forget this, because it’s how peace between the great powers was kept for 40 years during the Cold War. A nuclear attack from either side was deterred by the threat that the other side would retaliate by blowing up the planet — a threat that it would have been criminally insane to act upon.

Hence Auberon Waugh’s remark in 1973 that “it is one of the most unpleasant parts of any American President’s job that he has got to pretend to be mad, or the nuclear deterrent would lose all credibility.”

The problem for Costello (and what made nuclear deterrence such a dangerous game) is that overblown threats eventually lose credibility.

The threat-maker has to carry out a threat occasionally, even if the short-term costs outweigh the benefits, because otherwise subsequent threats won’t be believed.

Costello could have challenged in 2003, when John Howard reneged on his “when I’m 64” promise. But having failed to do so, he was less likely to be taken seriously the next time. And after failing to carry out the threat in 2006, it’s even less likely that further threats will be believed now.

In a way, it’s a compliment to the Treasurer’s judgement that the Howard camp realised he would never be crazy-brave enough to act on his threats. If he’d had more of a reputation for recklessness, he might have been prime minister by now.