Despite its confident saber-rattling, Israel’s concern is growing that the country is vulnerable to a devastating counterstrike if it attacks Iran’s nuclear program. An announcement this week that a mobile rocket-defense system soon will be built just outside Tel Aviv - where Israel’s sprawling military headquarters sits smack in the middle of office towers, museums, night spots and hotels - caused some jitters. Israeli officials cite intelligence reports that Tel Aviv would be a main target of any attack. Increasingly, the debate in Israel is turning to whether a strike can do enough damage to the Iranian program to be...