US President Donald Trump made a very serious miscalculation when he announced to the world that he had canceled an attack on Iran because he considered the proposed US response to Iran's act of aggression to be "disproportionate."
"...regarding Israel's war against its enemies, also enemies of G-d, our sages said (Tanchuma, Shoftim 15): “When you go forth to battle against your enemies” (Deut. 20:1): What do the words, “against your enemies” add? G-d said, “Go forth against them as enemies. Show them no mercy, just as they show you none.” Our sages said, “Go forth against them as enemies,” not as friends. These evildoers will never care about your welfare, so you should not care about theirs. This is the ethical, philosophically based law of G-d. Regarding one's enemy, there is no room for love and forgiveness. On the one hand, he will not show loving pity for Israel if he has the opportunity to dominate it.The Israeli government follows the same warped standard of 'fairness' with regard to attacks emanating from Gaza. Every decision is guided by a tit-for-tat strategy. It's immoral, demoralizing and cruel. If a country is attacked and has the power and the means to deal their enemy a mortal blow, it is the very height of stupidity not to do so.
As our sages said (Yalkut Shimoni, Devarim 20:923, quoting Eileh HaDevarim Zuta): “When you go forth to battle against your enemies”: If you take pity on them, they will go forth to battle against you. It is like the shepherd who used to watch his sheep in the forest. He found a wolf cub and took pity on it, letting it suckle from the goats. His employer saw this and said to him, “Kill it! Take no pity on it or misfortune will strike the flock.” The shepherd did not heed him. When the wolf was grown, it would see a lamb or kid and kill it. His employer then said, “Did I not tell you to show no pity?” Moses said the same to Israel: “If you take pity on them, then 'Those that you let remain shall be as thorns in your eyes' (Num. 33:55).”
(See War of Attrition)