If it comes to massacres by the Mubarak regime, the US would firmly support him

This is about Israel, not about Mubarak.  The Israeli strategy in the Middle East has been firmly set on the continuity of the Sadat-Mubarak dictatorship.  There is much about the security of Israeli terrorism and occupation there.   The US understands that: and Mubrak knows that the US understands that too.  Expect a tightening of the siege of Gaza by Mubarak.  But if Mubark needed to massacre people in the streets, the US administration AND Congress would stand firmly behind Mubarak.  No question about it at all.  That attests to the bravery of Egyptian protesters: but they know what they are facing.  A Mubarak Monster.