CAIRO (Reuters) - Mohamed Morsy's victory in Egypt's presidential election takes the Muslim Brotherhood's long power struggle with the military into a new round that will be fought inside the institutions of state themselves and may force new compromises on the Islamists.
Stripped of many of its powers in the past week by the generals, the presidency Morsy is set to assume bears little resemblance to the one that Hosni Mubarak was forced to give up 16 months ago after three decades in charge.
That, together with a host of other factors, will put a break on how much Morsy, 60, will be able do in office.
Despite the historic magnitude of his victory - Morsy is Egypt's first freely elected leader and comes from a group outlawed for most of its 84-year existence - the chances of rapid changes in domestic or foreign policies appear faint.
Some of Morsy's more ambitious campaign pledges - his promise to implement Islamic sharia, for example - could well be shelved as the realities of office bite in a country that is deeply divided by the idea of Brotherhood rule.
As things stand now, Morsy does not even have a parliament to pass such legislation, even if he wanted to, although he will form both a presidential administration and appoint a prime minister and government. But the Brotherhood-led legislature, elected in January, was dissolved by the generals who have given themselves the power over legislation in its absence.
"Morsy's thinking was to get a foothold in the presidency and to use some of the informal powers that come with it - being the figurehead - to try to slowly accumulate powers to offset the military council," said Joshua Stacher, an assistant professor of political science at Kent State University.
"But what we have is a situation where the civilian, elected president will be taking the blame for Egypt's continuing problems, while the military council is above such criticism. It has become king-like," he said.
A constant theme of Egyptian history since army officers overthrew the king in 1952, the old rivalry between the Islamists and the military looks set to continue.
Even with its flaws, the presidency and the popular mandate it represents adds a string to the Brotherhood's bow as it gets ready for a struggle of even greater importance than the historic presidential election: the fate of a new constitution which will define Egypt's new system of government.
"The Muslim Brotherhood will take what they've got - a prize unimaginable to them 18 months ago. An imperfect presidency is way better than none at all," said a Western diplomat in Cairo.
"It's part of the new and delicate act of political compromise - part of Egypt's new cohabitation."
The yet-to-be written constitution will set out the extent of the presidential powers and the role of the military establishment, which the Brotherhood has said appears bent on making sure it is written in a way that protects army interests.
The Brotherhood had secured a decent say in the body that started work on the constitution last week. But the generals have also given themselves new powers over the process, including the right to set up a new constitution-writing body if the existing one is deemed to have failed.
A court, which sits on Tuesday, is to review a challenge to the legitimacy of the current drafting body.
And beyond the Brotherhood's struggle with the military lies another, potentially more challenging opponent for Morsy: the entrenched interests of agencies accustomed to doing things the old way. The so-called "deep state", including shadowy security agencies, will likely prove a major obstacle to change.
"President Morsy will struggle to control the levers of state. He will likely face foot-dragging and perhaps outright attempts to undermine his initiatives from key institutions," Elijah Zarwan, senior policy fellow at the European Council on Foreign Relations, said in Cairo.
"Faced with such resistance, frustration may tempt him to fall into the trap of attempting to throw his new weight around," he added. "This would be a mistake."
With a convincing, but far from crushing, 3.5-percentage point victory margin over Ahmed Shafik, Mubarak's last prime minister, Morsy immediately faced calls to make overtures to those who have been alarmed by the Brotherhood's rise.
In his first remarks as president-elect, he promised to be a president for all. He has pledged to build a broad administration - something analysts say would be a major asset to the Brotherhood as it pursues its reform agenda.
That process of forming an administration starts on Monday. Among names cited by senior Brotherhood officials, reformist former U.N. diplomat Mohamed ElBaradei has been sounded out on his interest. Shafik also said he was available, if asked.
Brotherhood activists have promised to extend street protests to force the generals to backtrack on the recent decisions that have taken some of the shine off Morsy's win.
But behind closed doors, the Brotherhood will also continue to seek compromise with the generals, as they have done in the past few days since the constitutional decree was issued.
"Nobody should doubt there is going to be deal-making," said Shadi Hamid, director of the Brookings Doha Center.
"The Supreme Council of the Armed Forces still has the tanks and guns and the Brotherhood still understands that," he said. "There has to be some temporary power-sharing agreement.
"There has to be give and take."
Mustapha Kamal Al-Sayyid, a professor of political science at Cairo University, said: "There are some very important, divisive issues between them.
"It is important for Morsy to either resolve them or to accept some compromise, because otherwise his rule will be marred."
Editing by Alastair Macdonald