In his first speech as the presumptive Democratic presidential nominee, Barack Obama pledged unwavering support for Israel, vowed to use military force - if necessary - to keep Iran in check, and endorsed the idea that any peace deal between Israelis and Palestinians must preserve Israel as a Jewish state with Jerusalem as its capital.As president, "I will do everything in my power to prevent Iran from obtaining a nuclear weapon," Obama told a standing-room-only crowd at a meeting of the American Israel Public Affairs Committee, a powerful grass-roots lobbying group. "Let there be no doubt: I will always keep the threat of military action on the table to defend our security and our ally Israel."But Obama insisted that US military force is a last resort, only after every diplomatic avenue has been exhausted. And he defended his support for direct talks between the United States and Iran at the time and place of his choosing.