Israelis vote next week in an election seen as a referendum on the tenure of Prime Minister Benjamin Netanyahu, who could lose but still secure a new term in power.
Netanyahu, 65, called for the March 17 vote late last year as his coalition government teetered on the brink of collapse. It will be Israel's third election since 2009 and the premier's biggest challenge after six years at the helm.
"Netanyahu is the big question here, after having been in power for so long," said political analyst Tamir Sheafer.
The veteran rightwing leader is not certain to win the vote, with the most recent opinion polls giving a three-point lead to the centre-left Zionist Union led by Isaac Herzog.
But with polls showing Netanyahu's natural allies on the right likely to win the most seats, he has a clear advantage in piecing together a coalition with smaller parties.
On Thursday, Netanyahu conceded his opponents could win and warned that would threaten Israel's security.
"Our security is at great risk because there is a real danger that we could lose this election," he told the Jerusalem Post.
He said an opposition victory would "cause such a monumental shift in policy that it is a danger."
The next prime minister will have to deal with a series of daunting domestic and foreign policy challenges including Iran's nuclear programme, repairing ties with the United States and maintaining economic growth.
And then there are the tricky issues of ties with the Palestinians following the collapse of peace talks last year, instability left over from the 2014 Gaza war and a looming legal challenge at the International Criminal Court.
- Contrasting personalities -
As in previous elections, Netanyahu has framed himself as the only candidate capable of protecting Israel from Iran and the threat of Islamic extremism.
Last week, he made a bellicose address to the US Congress in which he pilloried nuclear talks between world powers and Tehran, in a move that put severe strain on Israel's relationship with the White House.
It was also aimed at sending a message of strength to voters back home. But analysts are unconvinced that sabre-rattling is the best way to win votes this time.
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"It has been a while since Israelis wanted a 'strongman'; we want the next leader to be charismatic and to solve problems," Sheafer said.
Netanyahu's only realistic challenger is Herzog, who in pushing for social justice and fresh talks with the Palestinians is offering voters a stark alternative.
A shrewd diplomat who has held several cabinet posts, Herzog has every bit the political pedigree to be the next prime minister but has been accused of lacking charisma, Sheafer says.
Still, with many Israelis feeling the pinch from the soaring cost of living and a housing crisis, Herzog and his number two -- former chief peace negotiator Tzipi Livni who heads the centrist HaTnuah faction -- may have found a stick big enough to beat Netanyahu with.
- Arabs united -
When the polls open at 7:00 am (0500 GMT) on Tuesday, more than 5.8 million people will be able to vote in a race contested by 25 lists.
Under Israel's proportional representation system, any party can enter parliament if it receives more than 3.25 percent of the vote.
Until last year, the threshold was two percent but legislation to raise it prompted Israel's main Arab parties to unite into a Joint List, with polls predicting they will win around 12 seats in the 120-member Knesset.
Several polls this week predicted the Zionist Union would win 24 seats, putting them three or four ahead of Netanyahu's Likud which has seen a recent erosion in support.
The last time Israel elected a Labour leader was in 1999.
The polls close at 10:00 pm and results are due early Wednesday, after which President Reuven Rivlin has a week to ask the party leader best placed to form a government to do so.
The leader then has 28 days to present a government lineup.
"With 24 or 25 seats, the party of the next prime minister will be the weakest in all Western democracies. That's less than 20 percent of the vote," said political scientist Denis Charbit.
"The leader's party is going to be a minority in its own government."
Moshe Kahlon, a popular former Likud minister, has so far hedged his bets about which candidate he would back, making him and his centre-right Kulanu party -- which is slated to win eight seats -- a potential kingmaker.