How to have your cake and eat it, Israeli-style

Further to my tweet about Israel earlier, it does seem extraordinary that Peres can call on the leader of the second-largest party to form a government on the strength of backing from small ultra-right parties, and yet Netanyahu can then immediately attempt to sideline those parties and instead bring Kadima into his coalition. Surely in these circumstances the nature of the coalition should be settled before the premiership? If Netanyahu feels it's so essential to form a centrist/centre-right coalition with the largest single party, he should surely be forced to accept the leader of that party has the stronger claim to hold the post of Prime Minister.