Might Shas, UTJ, and/or Yisrael Beitenu bolt the coalition when convergence comes before the Knesset? Sure, that may well happen. However, with Kadima, Labor, Gil, Meretz, and the Arabs there are roughly 70 votes in favor in the Knesset and, based on the disengagement vote, don't count on Shas to vote no either.
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The only message I took from the elections was that the Israelis were fed up with all the politicians. Between the record low turnout and the big win for the pension party it seems that the Israelis don't believe anyone has the answer for their military and diplomatic problems. By the way, it looks like they will get a heavy dose of socialism with Kadima, Labor, and Shas. Labor and Shas just want money for different constituencies. On balance it does not look too good.