In the early days of a recent war, the United States rushed to communicate with Israeli leaders who were meeting to plan a major attack on Hezbollah, a militant group based in Lebanon. The US wanted to warn them that their information might be wrong and that they needed to think carefully about their next steps.

On October 11, Jake Sullivan, the US National Security Adviser, managed to send a short note to Ron Dermer, Israel's Strategic Affairs Minister. The note warned against launching...