by Chris Bodenner

Simon Tisdall orients us with some background:

Egypt is not Tunisia. It's much bigger. Eighty million people, compared with 10 million. Geographically, politically, strategically, it's in a different league – the Arab world's natural leader and its most populous nation. But many of the grievances on the street are the same. Tunis and Cairo differ only in size. If Egypt explodes, the explosion will be much bigger, too.

Michael Scherer reminds us that Cairo was the site of Obama's historic address to the Muslim world:

Even though the Egyptian president Hosni Mubarak is an ally of the United States, it would be jarring if Obama makes no mention of this unrest in his speech tonight, or in some other public statement.

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