There has been no shortage of Egyptian precedents. Hosni Mubarak invoked Egypt's emergency law immediately after assuming office - and it stayed in effect for his entire 30-year rule. After his fall, the Supreme Council of the Armed Forces announced that it would monopolise parliamentary powers and the right to elect the constitutional assembly. We saw how that turned out.
When President Mohammed Morsi declared his own self-appointed powers on Thursday, protests were immediate. In the Nile Delta town of Damanhour, demonstrations left one dead and dozens injured. Thousands stormed Cairo's Tahrir Square, and by Sunday afternoon Egypt's main stock index had dropped nearly 10 per cent.
Mr Morsi has earned high marks for his foreign policy: his mediation between Israel and Hamas to end the bombing in Gaza last week was a remarkable victory for an Arab statesman, and earned rare praise from the White House. But Washington may have regretted those words after Mr Morsi turned around and made - by all appearances - a deeply antidemocratic pronouncement.
Yet foreign affairs, directed by the president, is relatively easy to shape compared to domestic policy, which must balance the interests of millions of Egyptians. Mr Morsi insists his new sweeping powers, which are supposed to be temporary, are necessary in a chaotic Egypt.
Perhaps that is true. Delays in drafting the country's constitution have made the process a farce, with a third of the drafters walking out last week. There is real doubt whether the judiciary, which is largely a holdover from the Mubarak era, will prosecute wrongdoers in the security forces. But obviously Mr Morsi has overreached.
What is at stake is Egyptians' trust - both in the president and in the new political system. As for Mr Morsi's political standing, he may find himself hamstrung. Three of his advisers stepped down yesterday, signalling the pervasive unease with the recent decision. On Friday, he told supporters he is "for all Egyptians". Given that he has been a Muslim Brotherhood stalwart for decades, this will be tough sell to many Egyptians.
The concern is not that his political party will triumph in future elections, but that its Muslim Brotherhood backers will resort to undemocratic or even illegal means to hold power.
It will take years for Egypt's transition to a representative democracy - this may be just one bump in a long road. But Mr Morsi would do better to reverse this decision than just rush forward.