NAPLES — As NATO bombs began to rain on Libya in March, President Obama and other Western leaders assured their war-weary publics that the campaign to protect civilians from Moammar Gaddafi’s crackdown would be over within weeks. Now the coalition’s springtime incursion has stretched to summer and Gaddafi’s resilience has startled the leaders who committed to the operation. Calls are growing to end it even as NATO pleads for more time. As the campaign enters its fourth month, NATO officials insist that it is succeeding and that Gaddafi will become the Arab Spring’s third casualty. But that will happen, they...