RUTHFULLY YOURS

Mr. Gantz’s Blue and White party won the most seats in the September elections, 33 to Likud’s 32, but Mr. Netanyahu was given the first chance to form a government because he had more support from other smaller parties elected to the 120-seat Knesset. He faced a deadline later this week to form a government or return the mandate.

Mr. Netanyahu’s announcement, on his 70th birthday, marks a setback for the prime minister who has earned the nickname “the magician” for his ability to wiggle out of tight spots in a political career spanning three decades. After the attorney general announced in February his intent to indict Mr. Netanyahu on corruption charges pending a hearing, Mr. Netanyahu campaigned on his security credentials and strong relationships with President Trump, Russian President Vladimir Putin and other world leaders. But he failed to form a government after the April elections, triggering the second vote.

“I made every effort to bring Benny Gantz to the negotiating table. Every effort to establish a broad national unity government, every effort to prevent another election,” Mr. Netanyahu said Monday in a video statement. “Unfortunately, time after time, he declined. He simply refused.”

With a decision on whether Mr. Netanyahu will be indicted due in November or December, the Israeli prime minister might be further motivated to try to hold on to the premiership for as long as possible, analysts said, including by staying in the role during a possible third election.

Mr. Netanyahu said in the video message on Facebook that he would try to bring down any government Mr. Gantz tries to form that would rely on the support of Israel’s Arab parties. Mr. Netanyahu has floated the possibility that Mr. Gantz would form a minority government of fewer than 61 seats that would need the Arab parties’ support, though Mr. Gantz hasn’t said he would do that. Mr. Netanyahu has accused those parties of supporting terrorism and rejecting Israel’s existence as a Jewish state.

“I will stand as the head of the opposition and work together with my friends to bring its downfall quickly,” Mr. Netanyahu said.

In a statement Monday, Mr. Gantz’s Blue and White party embraced the opportunity to form the next government and try to end the country’s long period of political uncertainty.

“The time of spin is over, and it is now time for action,” it said, adding that it would try to form a “liberal unity government.”

Mr. Netanyahu blamed the breakdown in discussions to form a coalition on Mr. Gantz and another rival, Avigdor Lieberman, whose eight seats gave him a kingmaker role. The Israeli prime minister had been trying to form a unity government with Mr. Gantz’s Blue and White party, a centrist alliance led by three former chiefs of Israel’s military, as well as a bloc of religious and right-wing parties that have been his natural allies.

Blue and White has said it is trying to form a unity government with the two largest parties.

Mr. Lieberman has pressed for a unity government between Blue and White and Likud and has refused to sit with some of Blue and White’s other likely partners.

If Mr. Gantz fails, Israel will go to a third round of elections—unless 61 members of parliament recommend a third candidate to try to form a government. If that fails, Israel will hold a third round of elections.

Mr. Gantz’s party has refused to sit with Mr. Netanyahu while he faces corruption charges and also has opposed sitting with Israel’s religious parties. Mr. Netanyahu denies wrongdoing.

To form a broad “unity” government of at least the two largest parties, Mr. Gantz will need to either convince Mr. Netanyahu’s Likud to abandon its leader or go back on his promise not to include him in the government.

While Mr. Netanyahu is at a particularly vulnerable moment, he isn’t finished. His Likud party has a long tradition of sticking with its leaders and none of the party members have pressed for a leadership vote to replace him. Several have floated taking the reins of the party after he leaves.

“Likud is not ready to ditch Netanyahu,” said Mitchell Barak, a political analyst and director at Keevoon Global Research, a Jerusalem-based consulting firm. “Likud will punish that person and he won’t be head of the Likud.”

Eventually, the specter of a third election could change the equation, he said. Both Likud and Blue and White lost support after April’s vote and are likely to try to avoid another contest, he said.