JERUSALEM -- The two main challengers to Prime Minister Benjamin Netanyahu joined forces Thursday in a united front ahead of April elections, a dramatic move that upended the campaign and suddenly created the most serious threat to the Israeli leader's decade-long grip on power.
Retired military chief Benny Gantz and Yair Lapid, head of the Yesh Atid party, appeared together on live TV late Thursday to announce their partnership, saying they were putting aside their personal rivalry in a shared goal to oust Netanyahu.
"Something went wrong this past decade. Israel has lost its way," Gantz said. "Instead of separation, we offer unity. Instead of extremism, we offer patriotism. Instead of incitement, we offer national reconciliation."
Opinion polls on Israeli TV stations showed the new "blue and white" alliance jumping ahead of Netanyahu's Likud Party. Netanyahu, taking to the airwaves later Thursday, dismissed his challengers as "leftists" who will destroy the country.
Netanyahu is pursuing a fourth consecutive term, and opinion polls have forecast another Likud victory in the April 9 election.
But Gantz, a popular political newcomer, has emerged as a potent challenger since announcing his candidacy late last month. Both he and Lapid hold similar views on a host of issues popular with centrist Israeli voters, ranging from the economy to the Palestinian issue.
Gantz has the added attraction of being a former military chief, a key credential with the security-obsessed electorate. He also has enlisted two other former military chiefs, Moshe Yaalon and Gabi Ashkenazi, to join their ticket.
The two leaders reached their agreement after concluding that joining their two parties together would win more votes than if they ran separately.
"A winning team needs to be led. I wouldn't be standing here today if I didn't believe that Benny Gantz could lead us to victory and then lead the country," said Lapid, who put his own ambitions of becoming prime minister on hold to form the partnership.
Under their arrangement, the two agreed to a rotation leadership should they come to power. Gantz would first serve as prime minister and would then be replaced by Lapid after two-and-a-half years.
Opinion polls showed Gantz and Lapid leapfrogging over Likud, forecasting as many as 36 seats in the 120-seat Parliament for their new alliance.
But even if the joint list emerges as the largest party, it does not guarantee victory unless it can form a parliamentary majority with smaller partners. Thursday night's polls showed Netanyahu's right-wing nationalist bloc and the center-left alliance in a deadlock.
Netanyahu responded on live TV by branding his opponents "leftists" who planned to make concessions to the Palestinians and novices who will destroy the economy.
"Whoever votes for Lapid and Gantz votes for the left," he said.
He went on to list a series of his accomplishments, including building a wall along the Egyptian border to halt the flow of African migrants, lowering unemployment, and forging new diplomatic alliances, including in the Arab world. He also said he had helped persuade the Trump administration to scuttle the international nuclear deal with Iran and recognize contested Jerusalem as Israel's capital.
"They say the country is in a bad condition," he said. "It's never been in a better condition."
He then claimed Lapid and Gantz would conspire with small Arab parties to prevent him from forming a parliamentary majority.
"Tonight the decision is as clear as it ever was: a new left-wing government, weak, led by Lapid and Gantz, with a blocking majority of Arab parties, or a strong right wing government presided over by me," he said.
The two addresses laid out the contours for what is sure to be a nasty final stretch of the campaign.
Netanyahu will try to position himself as tough on security and the only man capable of leading the country at a challenging time, while his opponents will target his character and the hard-line religious and nationalist agenda he has promoted at home.
"For the first time since 2009, we have a competitive race for the premiership and this is the result of the emergence of this new centrist force," said Yohanan Plesner, a former lawmaker and president of the non-partisan Israel Democracy Institute.
"There are now, as a result of this unification, two, I would say, legitimate major parties ... (but) it's not a done deal," Plesner said. "I think Netanyahu is still more likely to win and to emerge as prime minister at the end of this election campaign, but it is a competitive race."
After a decade without a serious challenger, Netanyahu suddenly appears vulnerable.
Israeli police have recommended that Netanyahu be indicted in a series of corruption allegations. The country's attorney general is expected to soon make a decision on whether to file charges — a move that would throw the campaign into turmoil.
Netanyahu has indicated he will not step down if indicted, but some allies could put pressure on him to step aside as he fights the charges.
Netanyahu also faced heavy criticism for his decision to form an alliance with a small extremist faction that is inspired by the banned Kahanist movement, which dreamed of turning Israel into a Jewish theocracy and promoted a racist agenda that called for the forced removal of Palestinians.
Netanyahu has said smaller parties that do not have enough support to enter Parliament on their own should band together under his leadership to ensure Likud's continued rule.
Netanyahu's courting of such forces drew sharp condemnations from much of the Israeli mainstream, with Gantz accusing him of losing touch "with his Zionism and with his dignity."