There's a saying that, if it's round, and green on the outside, red on the inside, has black seeds, and otherwise looks like a watermelon - it most probably is a watermelon. The same could be said about Shas, that if it looks like an opposition party, sounds like an opposition party, and behaves like an opposition party - that's a sign it is an opposition party. Just as the most determined skeptic is invited to cut the watermelon open and take a bite to be convinced that what he has before him is a fruit and not a basketball - it's high time that Prime Minister Ehud Olmert wise up and understand that Shas' representatives are part of the coalition in order to foil the peace process he has initiated, and in this way they are undermining the raison d'etre of the government - at least in the way Olmert presents that government.

On Monday, Shas chair Eli Yishai tightened the noose on the political neck of the prime minister just a bit more: Having already forbidden Olmert from discussing the subject of Jerusalem as a "core issue" with the Palestinians, and having warned not to dare to even express a view that reflects willingness to discuss a compromise on Jerusalem - Yishai now demands that he completely stop the political talks with the Palestinians so long as Qassam rockets continue to be launched into Israel from the Gaza Strip. In the words of Deputy Prime Minister Yishai: "We need to end the negotiations and concentrate on ending terrorism."

In other words, this movement, whose ranks do not normally contribute to the troops who will be sent into the alleys of Beit Hanun and Jabalya, is giving the prime minister an ultimatum: If he does not immediately opt for the military option and relinquish, at least for now, the diplomatic process, Shas will leave the government.

Shas' demand pushes Olmert into a corner, and exacerbates the question raised by his insistence on remaining in his post even after the grave report issued by the Winograd Committee. Olmert has asked us to believe that it is not selfish motives and arrogance that lead him to continue managing the affairs of state; that his behavior is guided by the best interests of the country, as he views them, and which are encapsulated in his desire to reach an agreement with the Palestinians.

Basically, the premier has called on the public to forgive him for his poor performance during the Second Lebanon War, as he asks for the opportunity to calm the conflict with the Palestinians, and then create the conditions to resolve it. Now, along come Yishai & Co., who are drilling holes into the political flak jacket covering the prime minister: In their view, the direction in which he would like to lead the country is mistaken; they are suggesting, essentially demanding, that he go the opposite way - toward war.

In light of this situation, Shas' continued participation in the coalition is a farce. In the not-too-distant future, Shas will transform its views into a political move and leave the coalition. Even if Yishai's warnings are only tactical (to please Shas voters and fend off pressures from Benjamin Netanyahu and Avigdor Lieberman), they are building up to a binding public stance for Shas and creating expectations among its supporters.

Moreover, the views expressed by Yishai do reflect those of the party's constituents, and of Shas' spiritual leader, Rabbi Ovadia Yosef: They are not genuine partners to a willingness to make the necessary concessions for reaching an agreement with the Palestinians. Shas is an opposition party in practice, although it has sufficient audacity to continue benefiting from its place in government without accepting the collective responsibility that the position requires.

This approach is evident not only in its attitude to the question of the Gaza Strip and negotiations with the Palestinian Authority, but also in its demand for the restoration of stipends for children to the high levels they were at five years ago. Such a move would constitute an abandonment of the economic policy that encouraged people to join the work force. Shas also supports the initiative of United Torah Judaism that has called for an exemption for the Haredi education system from the requirement to include in its curriculum core subjects like math and English.

During the 25 years it has been involved in public life, Shas has managed to be "part of," but always from the outside: In its ideological view regarding the relationship between state and religion, it is hardly different from UTJ, which has consciously avoided being part of coalition governments, while in practice, Shas has exhibited great eagerness to be as close as possible to the pie. The choice carries with it obligations, certainly during times of difficult decisions, and if it adopts mutinous views - it should just get out.