If Israel considers itself in a battle for its life, its longtime prime minister, Benjamin Netanyahu, is battling for his reputation and his legacy.

After leading Israel for nearly 16 years in total and priding himself on bringing the country prosperity and security, Mr. Netanyahu, 73, now confronts the vivid failure of his own policies toward the Palestinians — presiding over what many Israelis are calling the worst massacre of Jews since the Holocaust.

The Hamas breakout from Gaza and incursion into Israel proper, killing hundreds of civilians as well as soldiers, is all but certain to mark Mr. Netanyahu’s legacy no matter the outcome of the fierce war he now promises against Hamas.

On Tuesday, under pressure to do so, Mr. Netanyahu struggled to try to negotiate a unity government that included some of his main rivals, most of them experienced military officers. But disagreements continued over their demands for a smaller security cabinet to administer the war, which would sideline some of Mr. Netanyahu’s most controversial ministers.

Most assume Mr. Netanyahu will keep his post for now. But Moshe Yaalon, a former army chief of staff and minister of defense, demanded that Mr. Netanyahu pay the price of his failure and resign, he said in a Facebook post.

Amit Segal, a political columnist for Yedioth Ahronoth and one of the journalists considered closest to Mr. Netanyahu, said the prime minister could not escape blame for the systemic failure, and for a policy of tolerating Hamas to try to stabilize Gaza.

“I can’t tell when, but it will make it very difficult for him to survive politically,” Mr. Segal said.

After the 1973 Yom Kippur War, when Israel was also taken by surprise and attacked by Egypt and neighboring Arab countries, but successfully fought back, there were thorough inquiries and political consequences. “I think that, like 1973, this war will end without a single figure, both politically and militarily, in the place they were on Oct. 6,” Mr. Segal said.

“Israeli history teaches us that unsuccessful wars lead to a change in government,” he said. “Israeli history is clear about the future to come.”

How the war ends will matter, of course, but only up to a point. Even a smashing victory is not likely to erase the initial failure. But Mr. Netanyahu, a good politician, knows that Israel exists to defend the Jewish people. He knows that Israelis want to eradicate Hamas, and he is already casting aside his usual caution to try to lead a significant war in Gaza and, if necessary, in Lebanon. Only a successful war can mitigate the lasting damage already done.

“Right now, Netanyahu is focused on damage control,” said Mazal Mualem, who recently wrote a biography of the leader. “In my opinion, he understands that he won’t be able to continue after such a devastating failure and, therefore, he is focused on achieving military and diplomatic success during this war.”

Mr. Netanyahu is now fighting for his legacy, Ms. Mualem said. “The thing he always feared most has happened — he fell asleep on the job and failed to maintain Israel’s security. It’s his nightmare come true.”

At the same time, Mr. Netanyahu is regarded as Israel’s most accomplished politician, with a deep understanding of a political system that has tended to shrink the center and the left in recent decades and who “thinks in Mideastern terms,” said Haviv Rettig Gur, a political analyst for The Times of Israel, an online publication.

“We are less a conservative France and more a very liberal Lebanon,” he said. “And Netanyahu has understood that in ways others have not, and that has protected him.”

He has traditionally campaigned on division and, once in government, tried to do damage control and heal the wounds.

But that has been harder in his latest term as prime minister, beginning in December 2022. To form a government — and receive immunity from a trial on charges of corruption — Mr. Netanyahu had to partner with far-right and ultrareligious politicians and parties that he had previously shunned. Until now, he is leading the most far-right, ultranationalist and religiously conservative government in Israeli history.

He made two controversial figures important ministers — Itamar Ben-Gvir, the minister of national security, and Bezalel Smotrich, the minister of finance and junior defense minister. Both want more settlements in the occupied West Bank and harsh policies toward Palestinians; both have given tacit approval to violence against Palestinians.

At the same time, Mr. Netanyahu pushed for a judicial overhaul that would weaken and politicize the Israeli Supreme Court, a move that has led to months of huge demonstrations in the streets.

These policies are now criticized as dividing Israelis and diverting government money and attention away from security and tying up the army in trying to keep West Bank settlers and Palestinians from violence.

Mr. Netanyahu even dismissed warnings from Yoav Gallant, his minister of defense, that his government was recklessly stoking conflict in the West Bank by antagonizing the Palestinians, saying they merely reflected the criticism of the political opposition.

Even Mr. Netanyahu’s achievement to expand Israel’s recognition in the Gulf with the Abraham Accords, and to try to negotiate recognition with Saudi Arabia, supported by President Biden, was seen by some as dismissing the concerns of the Palestinians and perhaps leading Hamas to try to remind the world that it could not be ignored.

Whatever the back story, this latest horrible violence has intensified a sense among Israelis that their institutions, even the fabled military and intelligence ones, are incompetent.

That feeling is being expressed even among the loyal voters in Mr. Netanyahu’s base — many of whom lived in the kibbutzim near Gaza that have been terrorized and destroyed.

“Israel suddenly looks vulnerable, and Israelis are losing confidence in the competence of their own institutions,” said Mark Heller of the Institute for National Security Studies in Tel Aviv. “And if Israel is losing confidence, its enemies are gaining confidence.”

Mr. Netanyahu benefits for now from Israeli unity in the face of this challenge, and from his reputation as an experienced leader who can be calm in a crisis.

Ze’ev Elkin, a member of the Knesset who was close to Mr. Netanyahu, and who served in his governments before breaking with him three years ago, nonetheless praised his leadership.

“I saw Bibi in complex situations of the state of Israel, and in many tests, he is a talented, experienced person,” Mr. Elkin said, referring to Mr. Netanyahu by his nickname. “We had disagreements, but he is a person from whom I learned a lot.”

But Mr. Netanyahu changed in 2019 and became more convinced of his indispensability, Mr. Elkin said. “I saw that his personal consideration prevails over the national considerations in making decisions.”

Many leaders toward the end of their long years in power, he added, move “from ‘I am the best leader for the country at this time’ to ‘The most important thing for the country is that I lead it, and the most important thing is that I lead the country’ — and he fell for it.”

Dahlia Scheindlin, an Israeli political analyst and pollster, suggested that a politically divided Israel would continue to split. Half the country will want Mr. Netanyahu “to be put before a special investigating committee and live out his days in ignominy, while the other half will say that this proves everything we ever said, that you on the left and your ideas of peace weakened us, and you should live out your days in ignominy,” she said.

But for now, Israel is united by the war. What comes afterward is not relevant, Mr. Elkin said. “He is the prime minister. We have many disagreements, but all this should be put aside for the time of war.”

Natan Odenheimer contributed reporting.