So why is Aoun calling for demonstrations?
Aoun is very much aware of the internal Lebanese political powers to know which buttons to push for his own benefit.
After the Formation of the current government, Aoun was stuck amidst a power struggle, and he was offerred a miserly cut in the cabinet for his participation. Aoun's decision at that time was that he deserves whatever the number of seats he has in the Parliament, percentage wise. Seniora & Co. said: No deal. Aoun said: Then I don't want anything, and I will be in the opposition. At that time, the government had an agreement with hizbullah, and the party of God was awarded seats in the cabinet for their participation, along the seats that Amal got. Then, there was the great divide between 14th of March and 8th of March. After this divide, Aoun stepped in and signed a paper of agreement with Hizbullah.
So let us put it this way: You have 2 opposing groups, one in power, the other in opposition. Seniora & Co VS Hizbullah & Co. Hizbullah & Co. are not a majority in this formula, they are a minority. But when you introduce Aoun into the equation, the formula changes. Aoun can decide who the majority is. If he sides with Hizbullah and Co., then they become the majority, if he sides with Seniora & Co., they become the majority. He has managed to put himself in a very useful position.
Let us just remember that it is a fight for power, on all sides. Aoun was willing to side with 14th of March since day 1. But even before he came back to Lebanon, he was fought and sidelined by that camp. Jumblat called him the Tsunami, knowingly, because he knew that if he is not "sized", he will rise to become the most powerful man in Lebanon. Therefore, March 14th war against Aoun has taken its toll. Now Aoun is back with a vengeance. His popular base extends beyond the Christian street. In the Shiaa community, he ranks in popularity above Nabih Berri! He also knows that neither Hizbullah nor Amal want Syria back in Lebanon, yet, they will not declare it. March 14th knows this fact also, but plays it to its favor. By accusing Hizbullah & Co. of being Pro Syrian, they keep their base intact.
So now, Aoun is calling for demonstrations on friday to establish a government of National Unity. What this means is that He wants to take his share in the ministry, the same one that was denied for him in the first place. What does this mean in terms of power share. It means that the numbers in the cabinet should reflect those in the parliament, but in this case, the cabinet number of votes only need a third to stop a law from passing. So, if Hizbullah & Co. get their fair Share, Seniora & Co. get their fair share, and Aoun gets his fair share,, March 14th is in big trouble, because, every time they want to pass a law, they have to "talk" to the other members of the cabinet, and in the case of the tribunal, Hizbullah and Co. will not anger Syria, therefore, they are under the mercy of Aoun's approval, and Aoun has a price for this approval.