Sharif's political base is the group of lawyers who have been angered, all along, by Chaudhry having been deposed (impeached?) by the Musharraf government.
Evidently, under the threat of a major protest, Zardari has decided to reinstate Chaudhry to the Supreme Court:
"The Pakistani government agreed early on Monday to reinstate the independent-minded former chief justice of the Supreme Court, a stunning concession to Sharif, who had been heading toward the capital in a convoy threatening to stage a mass protest over the issue after he broke free from house arrest at his residence near Lahore."137. When did the relationship between Zardari and Sharif break down? I thought they were more or less getting along and I seem to recall a smiling picture (from last summer?) in which Sharif is congratulating Zardari for his election as President.