ISLAMABAD:  Prime Minister Nawaz Sharif on Thursday telephoned former president and Pakistan People's Party co-chairman Asif Ali Zardari and discussed prevailing political situation with him. Both the leaders also exchanged views on the PTI's Azadi March and Tahirul Qadri's Inqilab March. They agreed that they would not compromise on sanctity of the Constitution and no stone would be left unturned to safeguard the democratic system.