Morsi and the brothers are now vulnerable to their own success. They now must govern, manage and produce. And to do that effectively in a country like Egypt is no small achievement. In short, its all but impossible to meet the expectations that have been rising ever since Mubarak was ousted.
The brothers may have maneuvered themselves into the worst of all possible situations. They wont succeed in relieving Egypts crushing economic problems any more than Mubarak did, but in the process of trying to manage, they could compromise their principles and lose their ideological cachet. To maintain security in Sinai they may be forced to confront fellow Islamists, and keeping control over the border with Gaza could bring tensions with Hamas.