The most critical issue to be decided by the upcoming election came clear last week, yet it seems to have gone virtually unremarked. It isn’t tensions in the north, terror in Tel Aviv, Iran’s nuclear program, relations with America or any socioeconomic issue. Rather, it’s whether Israel will unilaterally withdraw from the West Bank.There have been hints of this for a while. But the clincher was last week’s announcement by the Labor-Hatnuah joint ticket – the self-proclaimed “Zionist Camp” – that its candidate for defense minister, should it form the next government, is Amos Yadlin.Yadlin is probably Israel’s leading advocate of unilateral withdrawal. He has used his current post as head of the Institute for National Security Studies to push the idea relentlessly, in forums ranging from briefings for Israeli reporters to articles in prestigious American journals. And it’s highly unlikely that someone of Yadlin’s stature – a former director of Military Intelligence who now heads one of Israel’s most prestigious think tanks – would agree to be any party’s candidate without assurance that his flagship policy would be on the table. Someone like Yadlin doesn’t enter government just to decide whether the IDF should add or cut another tank brigade. Granted, both Labor leader Isaac Herzog and Hatnuah leader Tzipi Livni would prefer a final-status agreement with the Palestinians, so any government they form would first try to reach one. But every round of final-status talks for the last 20 years has ended in failure, and the Herzog-Livni effort is unlikely to fare better. And once the talks collapse, it would be time for Yadlin’s Plan B – unilateral withdrawal from 85% of the West Bank.Indeed, Livni hinted as much in a Jerusalem Post interview last week. Asked why she thought yet another round of talks with Mahmoud Abbas would do any good, she replied, “The real question for me as an Israeli leader is not who is to blame, but how can we move forward in accordance to the vision of two states for two peoples, that represents the Israeli interest. Assuming that Abbas chose a strategy of going to the UN and International Criminal Court against Israel, as an Israeli leader we need to find a way to move forward – whether with him or in another direction.”In other words, if an agreement with Abbas is unattainable, Israel needs to find “another direction” through which to advance toward two states. That’s Yadlin’s position as well – and in his view, that “other direction” is unilaterally quitting most of the West Bank.Still, polls currently show Labor-Hatnuah winning only about 24 Knesset seats (out of 120), so it would need support from several other parties. And since polls also show that most Israelis oppose leaving the West Bank unilaterally, such a Knesset majority would surely be hard to find, right? Wrong. It would be depressingly easy.First, there’s Moshe Kahlon’s Koolanu party, whose diplomatic platform is being drafted by another leading advocate of unilateral withdrawal: the party’s number four, Michael Oren. Like Yadlin, Oren has pushed this idea in repeated articles and interviews in both Israeli and American media outlets. And someone of his stature – a former ambassador to Washington and acclaimed historian – is similarly unlikely to have joined any party, much less a brand-new, untested one, without assurance that his flagship policy would be on the table. So that’s another eight or nine votes in favor.Meretz and the Arab parties will vote for any withdrawal, even if they’re outside the coalition; as evidence, see the 2005 disengagement from Gaza. That’s another 17 or 18 votes.And United Torah Judaism can always be bought, just as Ariel Sharon did when his government was in danger of falling over the Gaza pullout. Then, UTJ’s price for rescuing the government was NIS 30 million. It would presumably demand more for the West Bank, but there’s no reason to think Labor-Hatnuah won’t pay. So there’s another seven votes. Shas voters lean right, but party chairman and strongman Aryeh Deri leans left. It was Deri who, by all accounts, persuaded Shas’s founder and spiritual leader, Rabbi Ovadia Yosef, not to oppose the 1993 Oslo Accord. Later, after Eli Yishai replaced Deri as party leader, Shas opposed the Gaza disengagement. But since then, Yosef has died, Yishai has been forced out and Deri’s control over Shas is absolute. Another six to nine votes.Finally, there’s Yair Lapid’s Yesh Atid. Before entering politics, Lapid avidly supported the Gaza pullout as a journalist. And in recent months, he has declared repeatedly that Israel must “separate” from the Palestinians and draw its own borders. In short, if another round of Israeli-Palestinian talks fails, he’ll back unilateral withdrawal. Another 10 or 11 votes.Add it all up, and that’s 72 to 78 votes in favor of withdrawal – far more than the 61 needed. Thus if Labor-Hatnuah forms the next government, unilateral withdrawal from the West Bank is highly likely.That’s grim news for the many centrists who are fed up with the current government but have no wish to repeat the disastrous experiment of the Gaza pullout in the West Bank, because it means such a pullout can be averted only if Prime Minister Benjamin Netanyahu remains in power. And that means voting for one of the only three parties certain to back him to form the next government: Likud, Bayit Yehudi or Yishai’s new party. Even Yisrael Beiteinu – which probably wouldn’t support a unilateral pullout – has indicated that it would prefer Herzog over Netanyahu as the next premier, and most of the other small parties have hinted the same. True, Labor-Hatnuah isn’t publicly touting unilateral withdrawal, and neither is any other party. But that’s because doing so would likely result in being trounced at the polls. So instead, withdrawal advocates are keeping quiet and hoping nobody notices that this is what’s at stake in the upcoming election.But it is. And therefore, anyone who doesn’t want the West Bank turned into a missile-launching pad like Gaza must vote for a fourth Netanyahu government – even if they have to hold their noses and swallow hard to do it.Evelyn Gordon is a journalist and commentator. Follow her on twitter here.