Punjab is the most populous province of Pakistan and the most important one in terms of the political impact on the federal government. It is often said that who rules the Punjab actually controls the governance in the Pakistan and right now the ruling strings of this all crucial province are controlled by the Pakistan Muslim League, and that is what is bugging intensely the PPP government in the Islamabad.
Asif Ali Zardari has never accepted the mandate of PML(N) in the Punjab and that is why he installed Salman Taseer as the governor in this province, and despite of the protests from the then coalition partners PML(N), he never withdrew the governor and Salman Taseer who is the open bitterest enemy of the Sharif brothers has been active in destabilizing the government in Punjab and impeding the Shahbaz Sharif in every possible way.
Now the Chaudhry Brothers of Gujrat are indecisive about their role, as Zardari wants to have a coalition with them, while most other Punjab PPP leaders are against it as they still believe that Pervaiz Elahi was involved in the Karsaz attack in Karachi on Benazir Bhutto, who was then later murdered in Rawalpindi.
Zardari just wants to kill Nawaz Sharif rule in Punjab and that is very dangerous.