In 2007, the historian Michael Oren released his book “Power, Faith and Fantasy” in which he prophesied that the United States would continue to pursue “traditional patterns of its Middle East involvement” in the years to come. Last month, Mr. Oren — still a historian but now also a former Israeli ambassador to the United States, and a current member of Israel’s Parliament — released “Ally: My Journey Across the American-Israeli Divide,” in which he refuted his own prophecy.

In Mr. Oren’s view, President Barack Obama did not pursue traditional patterns in the Middle East; instead, he claims that Mr. Obama changed America’s policies to the detriment of its staunchest ally in the region in a way that could imperil Israel’s future. This pattern culminated on July 14 when the Obama administration, along with several other countries, signed an agreement with Iran that is supposed to prevent it from acquiring nuclear weapons.

Some readers believe Mr. Oren committed an unforgivable sin by publishing a book that includes bold criticisms of Mr. Obama’s policies, an armchair psychoanalysis of the president’s motivations and complaints against notable Jews. But this is not the source of the outrage against him and his book; it is because Mr. Oren is seeking to redefine (or re-establish) what it means to be a true ally of Israel.

Mr. Oren has commended the Obama administration for its military “aid and support” for Israel. But he questions whether an administration that conducts “negotiations with Iran for seven months behind our backs, and trying to strike a deal that’s bad, very bad, for our security,” as he told me, can take credit for making Israel safer.

Critics have disputed Mr. Oren’s accounts of various events. They have questioned his timing and his motivations: “He is a politician trying to sell a book” was the response from the U.S. State Department. They also accused him of engaging in an “insensitive and unjustified attack on the president,” as the Anti-Defamation League framed it, because of his view that Mr. Obama’s outreach to the Muslim world may have stemmed from having a Muslim father. ...