Former Israeli justice minister Tzipi Livni and the center-left parliamentary opposition leader formed a joint election ticket on Wednesday that polls show could pose a serious challenge to Prime Minister Benjamin Netanyahu in March.
After months of infighting over Israel's handling of stalled U.S.-sponsored peace talks with the Palestinians, the 2015 state budget and nationalist legislation, Netanyahu last week fired Livni from his cabinet, in effect ending the conservative governing coalition in favor of an early election.
"I am here to create the force-multiplier that will change the government in the State of Israel," Livni told a televised news conference alongside Isaac Herzog of the Labor party.
Polls have predicted Netanyahu's rightist Likud party winning the vote called for March 17, with around 22 of parliament's 120 seats. Running separately, Labor and Livni's centrist Hatnuah party were seen trailing Likud.
But a December 4 survey by the Globes newspaper and a December 7 poll by the parliamentary television channel found that a joint Herzog-Livni list would edge the incumbent with 23 or 24 seats.
Herzog told reporters that, should they form the next government, he would serve as prime minister for the first half of the term and would rotate the role to Livni for the second.
"In the last election, two years ago, the centrist camp did not manage to stick together," Herzog said. "I promised to myself the day I was elected to head the Labour party that this time it will not happen - not on my watch."
He pledged to roll back Israel's international isolation over the Palestinian deadlock and nationalist policies and bring "security instead of fear, dialogue instead of hatred".
Some commentators doubted whether the alliance would work. Livni, originally a Likud member, has switched parties three times since 2005 and failed three times to secure the premiership.
Her latest move is to a party seen more as left-leaning than centrist in a country where hawkish sentiment seems dominant as regional security threats have proliferated.
"Extremists have taken over all the good prospects - all the good prospects of the Likud, which was once my home," Livni said. "They are turning our country into an isolated, boxed-in country, and an alienating one - even for its own citizens."
Likud was dismissive.
"Livni is nothing less than a demolition contractor whose only interest is a seat in the cabinet - not values," Likud lawmaker Miri Regev told the Ynet news site.
Netanyahu is expected to run in at least an informal alliance with the far-right Jewish Home party, which has been polling between 16 and 18 parliamentary seats.