As a hypothetical case, it would be an interesting one for a textbook on politics and morality:

A high-ranking politician promises his fellow countrymen that, under specified circumstances, he will resign from his position in government. These circumstances come to pass. Yet by the time they do, the politician regrets his promise because he now sincerely believes that his remaining in office is so crucial to the welfare of his country that he would be shirking his responsibility by leaving it. What does he do?

On the face of it, it’s an intriguing dilemma. And it’s the dilemma that Israel’s Labor Party leader and defense minister, Ehud Barak, says he found himself in last week after the final report of the Winograd Commission, the investigative body appointed to inquire into the conduct of the 2006 war against Hezbollah in Lebanon, at which time Mr. Barak was a private citizen.

Last April an interim report issued by the commission dealt harshly with the government of Ehud Olmert’s conduct of the war, leading to the internal party defeat and resignation of the former Labor leader, Amir Peretz, Mr. Olmert’s wartime defense minister.

Mr. Barak took over from Mr. Peretz with the solemn pledge that he would demand Mr. Olmert’s resignation, too, if the final report was as damning as the interim one. If Mr. Olmert did not resign then, he said, he would resign himself.

Now, over half a year later, the final report has been released and it’s indeed as damning as its predecessor. Yet Mr. Olmert has refused to resign and Mr. Barak has appeared before the cameras to announce that he isn’t resigning either. Yes, he knows he promised — but it’s because of the final report that he now feels he must stay on.

Israel’s army, the report declared, performed poorly in the war and is in urgent need of an overhaul — and no one, says Mr. Barak, is more qualified to oversee this than an ex-chief-of-staff and combat hero like himself. Noblesse oblige.

As much as he would love to keep his promise, his conscience won’t allow him to, especially because he is also needed at Mr. Olmert’s side to help push the peace process that was restarted at Annapolis. Let’s assume that all this is so. Let’s assume that Mr. Barak is really uniquely qualified to overhaul the army and that without him and the Labor Party, the government will fall apart and Benjamin Netanyahu will be returned to power in new elections, spelling the end of peace negotiations with the Palestinian Authority.

Let’s even assume that Mr. Barak’s fellow Labor cabinet ministers, who breathed a sigh of relief when he announced his decision, are not thinking about their own political fortunes or jobs but only about the future of the nation. Should Ehud Barak have broken his promise?

What, after all, is a promise compared to the fighting condition of an army or the prospect of peace? And what, especially, is a political promise? Don’t we all know that political promises are meant to be broken? As erstwhile a former prime minister of Israel, Levi Eshkol, once put it, “Just because I promised doesn’t mean I promised to keep my promise.”

And on the other hand: What kind of political system is it that takes it for granted that political promises need not be kept? What kind of society accepts such a system unprotestingly?

Promises, in the final analysis, are what all of human life is built on, starting with the simplest things. “Will you do the dishes tonight?” a wife asks a husband. “Yes,” says the husband. What are the chances of this marriage’s success if the morning after, the dishes still undone, the husband tells his complaining wife that promises are meant to be broken? What are the chances of a society’s success if everyday commitments — a parent’s promise to a child, a merchant’s quotation of a price to a customer, a businessman’s word of honor to another businessman — are routinely ignored?

What are the chances of an army’s success? Ehud Barak claims that he is needed to help rebuild the Israel Defense Force. But one of the IDF’s major problems in the 2006 war in Lebanon was that promises were not kept.

Divisional commanders told regimental commanders that such-and-such would be done and it wasn’t; platoon commanders told company commanders that they would be at such-and-such a place with their troops and they weren’t. There was a general breakdown in responsibility. By what authority is a politician who scorns keeping his promises going to remedy this?

By what authority can such a politician contribute to peace negotiations ? If you were a Palestinian negotiator and Mr. Barak made you a promise, would you believe him? Why should a politician who doesn’t keep his promises to his own people be expected to keep them to another? Some promises may indeed have to be broken. But no promise should be broken light-heartedly. Had Mr. Barak appeared before the cameras this week and spoken with genuine anguish about regretting a promise he should never have made, his breaking it might be forgivable. But instead he appeared with a grin and explained that he needn’t be held to account because circumstances had changed.

But circumstances always change. If they didn’t, there would be no need for promises to begin with.

No politician always tells the truth. But a politician who lies without compunctions is a politician who will never tell the truth when he doesn’t feel like it. Such a politician is not made to run a country. Ironically, Ehud Barak, who had nothing directly to do with the 2006 war, has ended up being the Winograd Commission’s main casualty. Israelis are not fools and he has lost all credibility with them. Although he may linger on in the Olmert cabinet for another year or two, his political career is, in effect, already over.

Mr. Halkin is a contributing editor of The New York Sun.