Nate Silver analyzes CNN's poll:

[S]upport for military interventions tend to be highest at the outset the so-called rally-around-the-flag-effect before declining until and unless some concrete objective is achieved. An important caveat is that the Libyan situation has evolved so quickly that we may still be midway through the rally phase. But if 50 percent approval is as good as the numbers get for Mr. Obama at the peak, overall support may turn negative unless Mr. el-Qaddafi is ousted fairly quickly.