As a shard of Israel, Netanyahu is challenged by the former protégé

But in order to challenge Mr. Netanyahu to lead the Likud in late 2019, Mr. Saar split to form his own party, called New Hope. This group offers a right-wing alternative to Mr Netanyahu for the upcoming March 23 elections, the fourth parliamentary vote in less than two years.

Unlike the Israeli elections of the last decade, where Netanyahu defended the challenges from the left and center, Mr. Saar poses a serious leadership challenge to his former right-wing mentor.

This poses a major threat to Mr Netanyahu, who faces criticism for his treatment of the coronavirus pandemic and his trial for corruption. If Mr Saar can continue to remove Mr Netanyahu’s support among right-wing parties in parliament, he could block the prime minister’s return to office.

“Everything is paralyzed,” Saar said in an interview at his Tel Aviv apartment, where he lives with his wife and two young children. Netanyahu “puts his personal interests above the good of the country,” he added.

It is unclear whether voters will trust an untested leader like Mr. Saar. Netanyahu, known as Bibi, has been in power for 15 years, through two wars with Hamas militants in Gaza and tensions with Iran. In recent months, Mr. Netanyahu has been involved in brokering diplomatic normalization agreements with Arab Gulf neighbors and presides over the world’s fastest Covid-19 vaccine launch.

Netanyahu’s sponsors dismiss Saar as a “political opportunist” who left Likud after losing support for the party.

“Saar brings together a group of bankers shouting ‘No Bibi’ from the stands as the Prime Minister leads the revolutionary ‘Operation Back to Life’ vaccination program which is a model for the world,” a Likud party statement said , which refers to vaccination campaign.

Mr. Saar’s political positions are similar to those of Mr. Netanyahu. He is a staunch supporter of West Bank Jewish settlements that have expanded under Netanyahu’s rule and have received criticism abroad, even in the past by President Biden.

Mr. Saar does not support the freezing of construction or the establishment of a Palestinian state, but would keep Netanyahu’s recent promise not to annex parts of the West Bank as part of diplomatic normalization agreements. Saar also opposes the return of the United States to Iran’s 2015 nuclear deal, which Biden has said he wants to renegotiate.

While Mr. Saar does not diverge much on Mr. Netanyahu’s policy, he says he would give a fresh start to the relationship with the new U.S. president. “I can deal with the Biden administration better than Netanyahu and do so while protecting our national interests and without contributing anything from the past that could disrupt this,” he said.

Netanyahu’s relationship with the Obama administration was strained, in part because of the U.S. nuclear deal with Iran, a staunch rival of Israel. In the last election, Mr. Netanyahu campaigned with huge billboards with photographs of him shaking hands with former President Donald Trump, calling the Republican leader the best friend Israel ever had in the White House.

“While they are from different political perspectives, it is not Netanyahu,” said Martin Indyk, a distinguished fellow of the Foreign Affairs Council. “Biden will want to have a positive constructive relationship with the Prime Minister of Israel.”

Although Mr Saar is pushing some supporters away from Mr Netanyahu, Likud is expected to continue to be the Knesset’s largest party, the Israeli parliament. The Yesh Atid party, led by centrist Yair Lapid, is also rising to the polls, complicating Mr Saar’s bid to frame the upcoming vote as a contest within the right wing.

The role of the ultra-Orthodox religious parties could be important in the race between Messrs. Netanyahu and Saar. Netanyahu has relied on them for political support. Mr Saar has not ruled out sitting with them in a future government, but so far these parties have indicated they will continue to support Mr Netanyahu.

For both politicians, navigating the support of the ultra-Orthodox is politically complex.

Israel’s ultra-Orthodox communities have resisted complying with coronavirus restrictions and clashed violently with police during protests against them. This has sparked anger among other Israelis and frustration among public health officials, who believe the continued breach of the rules is undermining the coronavirus effort.

To become prime minister, a candidate must muster a 61-seat majority coalition in the Knesset. A recent poll by an Israeli radio station shows that New Hope gets 17 seats for Likud’s 30. In this scenario, Netanyahu would not be able to form a ruling coalition as several parties refuse to form a coalition with the prime minister.

“Until Saar broke up, you reluctantly said that Netanyahu was the only game in town,” said Reuven Hazan, a professor of political science at the Hebrew University of Jerusalem. “Now, all of a sudden, Netanyahu is surrounded by enemies.”

The loss of Israel’s government office would push Mr. Netanyahu into dangerous territory. Last year he was charged with bribery, fraud and breach of trust charges in connection with allegations that he accepted expensive gifts from wealthy businessmen in exchange for official favors and offered two media moguls regulatory and financial advantages in return. of positive press coverage. He denies the faults. He failed in an attempt to gain parliamentary immunity that would have protected him from persecution while in office last year. His trial will resume next month.

If Netanyahu does not return as prime minister, he cannot serve in a governing coalition because of an Israeli law that requires the resignation of ministers if he is accused. This law does not apply to prime ministers. This setback would also complicate any efforts by the loyalists to pass a law that would protect Mr. Netanyahu from being tried while serving as prime minister.

Daniel Tarlow, a 48-year-old man who owns a catering business and lives in the West Bank Jewish settlement Elazar, said this time he would support Mr Saar instead of Mr Netanyahu because he believes the prime minister has not helped small companies during the pandemic.

“I’ve had enough of his politics and tricks,” Tarlow said of Netanyahu. “I think Saar says he’s a real Likud politician … If Bibi forced him to step aside, that means there’s enough substance for you.”

—Dov Lieber contributed to this article.

Write to Felicia Schwartz to [email protected]