As the Egyptians mount their challenge to the regime of Hosni Mubarak the man we keep thinking of is Ariel Sharon. He was the guest at the first editorial dinner of The New York Sun, held jointly with the editors of the Wall Street Journal. The date was November 2000, shortly before Mr. Sharon, in an election triumph at the start of the following year, acceded to the prime minister’s office at Jerusalem.

At one point, one of the editors asked the general which country in the Middle East, or anywhere else, he considered the most hostile to the Jewish state. Suddenly Mr. Sharon fell silent and so did the rest of the table. We remember thinking to ourselves: Iraq? . . . Iran? . . . Syria? . . . the Sudan? But when the general finally spoke the country he named was Egypt.

Some murmurs of surprise were heard. In theory, after all, Egypt and Israel had been at peace since Camp David. But the man who was about to become prime minister of Israel said that not only was Egypt the most hostile but it was also the most dangerous. It was the most populous Middle East country; it was influential in the Arab world.

Egypt had something like 12 divisions in its Army alone, one of the 10 largest air forces in the world, and millions of males of military age. In recent years, it had been armed and trained by America. That worried him. He didn’t belittle the fact that some Egyptians were prepared to gamble on peace. But the gamble had cost President Sadat his life, and the peace had been cold. In the order of battle, the great strategist had his eye on Egypt.

As Egypt is engulfed in flames, we can’t help thinking of Ariel Sharon’s warning. He was prepared to treat with Mr. Mubarak, and did on a number of occasions, but he never had illusions about him. He was well aware of Mr. Mubarak’s machinations against Israel in the United Nations, of his agitation against Israel’s nuclear capacity, of the fact that if Egypt really wanted to stop the arms smuggling into Gaza it would have.

At the prospect of Mr. Mubarak’s being toppled, his eyes would have been dry. The Israeli premier was anything but indifferent to the idea of democracy; he was a tribune of the idea that war rarely, if ever, erupts between democratic countries. And as a politician and founder of political parties, he was one of democracy’s most seasoned, even wiliest, practitioners.

All the more skeptical was he of the idea of rushing democracy, all the more aware of how democracy could be taken advantage of. It was an alleged democracy, if a false one, that Hamas manipulated to seize Gaza; it is of democracy that Hezbollah is seeking to take advantage in snuffing out the embers of freedom at Lebanon. Democracy can be defeated from within, as we witnessed in Iran.

Mr. Sharon understood the difference between real democracies — America’s, say, or Israel’s, with their free press, honest vote counts, and open ballots — and false ones, like that which returned Mubarak to power in September 2005 with 86% of the vote. “Egyptian Mirage” was the headline we put over our editorial at the time, which characterized the election as a “farce” and warned of what we called “misguided American policy toward Egypt.”

Our sense is that Mr. Sharon enjoyed, even on occasion thrilled to (as this newspaper has), President Bush’s pro-democracy agenda and the kind of rhetoric he unleashed when, say, he sent Secretary Rice to Cairo. He supported the war against Saddam Hussein and the campaign to liberate Iraq. But he was a man without illusions.

He would not have stood silent about the murders of Christians in Egypt, a silence our Youssef Ibrahim has been covering; Mr. Sharon would have comprehended those killings as a harbinger of greater trouble. In Egypt today Mr. Sharon would be watching intently for any realignment of forces or movement of Egyptian military units and armor. He’d have had his eye on the Suez Canal, any crossing of which by even small, incremental units — single tanks, say — would have riveted his attention.

For one of the things Ariel Sharon understood is that there is no logic for Egypt to be maintaining a military machine as large as the one it has built up in the past decade and a half, with American money and help. It is not required for intra-Arab struggles. Its only use other than to suppress Egyptians themselves, he would have understood, would be the one it has trained for, an eventual war against the Jewish state with which Cairo has maintained a peace that has been so strangely cold.

Sharon would have understood that America’s bargain with Mr. Mubarak failed to extinguish anti-Semitism in Egypt. He understood the implications in the fact that the old hatred has been allowed to infect a press that is controlled by the state. He would have understood above all else that the failure to act in the face of threats in any part of the Middle East invites attack from all sides, including from the colossus on the Nile.