"Sire, clear the square with gunfire or abdicate."
That was the message one of his generals gave the young czar Nicholas I in December of 1825, as thousands of civilians and soldiers massed in Senate Square to challenge his claim to the throne.
Nicholas gave the order, the cannons fired, and he and his heirs ruled Russia for another century, until Nicholas II was overthrown, and murdered by Bolsheviks.
Such was the moment Egypt's army faced on Wednesday, with thousands of backers of the Muslim Brotherhood encamped in Cairo, challenging its rule. The slaughter that ensued, 500 dead the first day and thousands wounded, means there is no going back.
The die is cast. The Egyptian army has crossed the Rubicon.
Egypt's generals cannot now hold elections that a coalition of the Brotherhood and Salafis might win. Were that to happen, many of them could wind up like the shah's generals, on trays in the morgue.
So where does Egypt, and where do we go from here?
While we Americans are babbling about a new politics of "inclusiveness," even some of the Twitter-Facebook liberals of Tahrir Square are coming to see Egypt as it is. Us or them.
And the one issue on which Egypt's Muslim militants and Egypt's militarists seem to agree is that the Americans cannot be trusted.
Two years ago, the United States celebrated an Arab Spring that began with the overthrow in Tunis and Cairo of dictators who had been our loyal allies. We then became the champions of free elections in Egypt, as we had been the champions of free elections in Palestine, until Hamas swept the board in Gaza.
When half of Egypt voted for the Brotherhood and a fourth for the more militant Salafis, we accepted the results and pledged to work with President Mohammed Morsi.
But Morsi failed as badly as Hosni Mubarak. So, when millions massed in Cairo's streets to demand Morsi's overthrow, we signaled our approval for a military coup.
Then, when Gen. Abdel Fattah el-Sisi seized power, imprisoned Morsi, jailed Brotherhood leaders and installed a puppet government, we refused to call it a coup.
Secretary of State John Kerry provided the comic relief by assuring us that the Egyptian army was "restoring democracy."
For two years, America has been loyal to no one, and consistent in nothing. Thus, Egypt's soldiers decided to do what they had to do to save their country. And if new elections are likely to produce a regime that threatens their Egypt, they will dump the democratic procedures rather than lose Egypt to the Brotherhood.
They will comply with our wishes to the extent that they do not imperil what the Egyptian army regards as vital. Gen. Sisi either did not believe we would cut off his military aid, or was willing to take that risk when he gave the order to fire on the protesters.
He read the Americans right. What do we do now?
As our interests dictate maintaining the peace between Egypt and Israel, keeping Egypt as an ally against Islamic terrorism, and protecting Christians, we cannot sever ties to the army that runs the country. In these goals, Egypt's military, no matter the brutality with which it behaved on Wednesday against the Brotherhood, is an ally.
But if we were to retain any credibility as the champion of peaceful protest, we had to signal that what was done by Egypt's security forces was done without our approval. President Obama did that by canceling the military exercises with the Egyptian army in Sinai.
Yet Egypt has problems we cannot solve. It is divided between secularists and fundamentalists, whose visions are irreconcilable. It is divided between a middle class and millions of poor for whom neither Mubarak nor Morsi was able to create any measure of prosperity.
Without constant infusions of aid, Egypt, a country whence the tourists and investors alike have fled, cannot create a robust economy until radicalism and extremism are in the past.
Egypt today cannot sustain itself. But America's role as primary foreign aid provider is coming to an end. Saudi Arabia, Qatar and the Gulf states are today sending many times the aid we are sending to Cairo.
Let them take the lead. The fate of Arab peoples is far more tied up in what happens along the Nile than is the fate of America.
While we do not know what will succeed in the Middle East, we do know what has failed. Nation-building in Afghanistan and Iraq has left us bleeding and near bankrupt. Our flipping and flopping in Egypt's turmoil has alienated all sides. Our wars have accomplished what?
Perhaps lowering our profile and shutting up would serve us better. This part of the world will be decades sorting out its future in light of the political, religious, ethnic and ideological forces unleashed by the Arab Spring and the rise of Islamism.
A phrase from the America of a century ago, when Mexico was in turmoil, comes to mind. Why not a period of watchful waiting?