JERUSALEM—Prime Minister Benjamin Netanyahu said on Sunday a newly formed Israeli coalition that is poised to unseat him was the result of “the greatest election fraud” in the history of democracy. He made his sweeping accusation at a time when Israel’s domestic security chief has warned publicly about the prospect of political violence. Netanyahu focused his allegations on a broken campaign promise from the man set to replace him as prime minister, nationalist Naftali Bennett. Bennett had pledged not to partner with left-wing, centrist, and Arab parties, but on Wednesday announced with opposition leader Yair Lapid that they had formed a governing coalition with factions from across the political spectrum. Under a rotation deal, Bennett will serve first as prime minister, followed by Lapid. No date has been set for a vote in parliament to approve the new government, which follows an inconclusive March 23 election, but it is widely …