The year 2013 was the year of the “brothers” in Israeli politics.

Two newcomers, Yair Lapid and Naftali Bennett, swept onto the scene, between them scooping up over a quarter of the votes in the elections. Despite their inexperience, the two built an alliance that checkmated Benjamin Netanyahu in the coalition talks and forced him to take them both on board, leaving the Charedi parties out.

As the year draws to a close, the pact between the two unlikely brothers is fraying. Whether or not it survives and how each of the brothers will fare on his own will be one of the defining features of Israeli politics in 2014.

Yair Lapid has the most to lose. His Yesh Atid confounded all predictions in the election by gaining 19 seats and becoming the second-largest party in the Knesset. But his voters have no tribal loyalty; they could disperse next time around and, if the recent polls are anything to go by, at least a third of them are already looking elsewhere. Mr Lapid was forced to take the poisoned chalice of the Finance Ministry and will be blamed for the cuts and tax raises. Now he is anxious to show he is doing something for his middle-class, left-leaning electorate. That is why his ministers are so eager to push ahead with laws on gay rights, to portray themselves as leaders of the peace camp and to insist on a national service law that includes criminal sanctions for Charedim who refuse to enlist.

This puts Yesh Atid on a collision course with Mr Bennett’s Habayit Hayehudi. The national-religious party is resolutely opposed to any concessions for the Palestinians, gay marriage and opening up a war with the Charedim. It is very difficult to see a coalition in which both parties succeed in realising their aspirations: as things look at the end of 2013, next year, one of them will have to leave government.

The falling out of the brothers hands a degree of control back to Prime Minister Netanyahu. He has two clear options now. Either support Yesh Atid, lose Habayit Hayehudi, and bring the Labour party, now under the leadership of the much more accommodating Yitzhak Herzog, into the coalition. Or, back Mr Bennett, force Yesh Atid out and welcome back his old friends in Shas and United Torah Judaism.

But both paths are fraught with difficulties. Sticking with Mr Lapid (and with Tzipi Livni’s smaller Hatnuah) could well split Likud because the great majority of the party’s Knesset faction is as right-wing as Habayit Hayehudi and will fight their leader tooth and nail if he makes significant moves towards a two-state solution. Not to mention his erstwhile partner Foreign Minister Avigdor Lieberman, who could use any diplomatic deal to break away from Likud and Mr Netanyahu.

Resurrecting his old right-wing- Charedi coalition would be much easier to do and secure his domestic flank but it would all but ensure a diplomatic crisis with the Obama administration and the EU.

The Prime Minister will naturally try to play for time, constantly reminding his troublesome partners and increasingly suspicious allies that Israel is facing a much larger threat in Iran. But his time is running out.