In Washington, Obama told the American Israel Public Affairs Committee (AIPAC) that if he were elected he would do "everything" in his power to prevent Iran from obtaining a nuclear weapon. He also gave assurances that Israel's security would be a top priority of an Obama administration.
AIPAC is one of the most powerful interest groups in the United States.
Obama told 7,000 of the group's members that the United States and Israel share many common values and interests, and said the security concerns of one are the security concerns of both: "Our alliance is based on shared interests and shared values. Those who threaten Israel threaten us. Israel has always faced these threats on the front lines and I will bring to the White House an unshakable commitment to Israel's security. That starts with ensuring Israel's qualitative military advantage."
The presumptive Democratic nominee devoted much of his attention to the country that many Israelis consider their greatest threat: Iran.
Both President George W. Bush and the Republican presidential nominee, Arizona Senator John McCain, have criticized Obama for saying that he would be willing to sit down and negotiate with Iran's leaders.
Addressing AIPAC, Obama appeared determined to erase any doubt that as president, he would take a hard line against the Iranian leadership, and President Mahmud Ahmadinejad in particular.
"The Iranian regime supports violent extremists and challenges us across the region," Obama said. "It pursues a nuclear capability that could spark a dangerous arms race and raise the prospect of a transfer of nuclear know-how to terrorists. Its president denies the Holocaust and threatens to wipe Israel off the map. The danger from Iran is grave, it is real, and my goal will be to eliminate this threat."
He emphasized that he would do "everything" in his ability to stop Iran from acquiring a nuclear weapon and "use all elements of American power" to pressure it into curbing its nuclear ambitions.
It was an assertion of Obama's belief in the potential of diplomacy, but also appeared tailored to emphasize his willingness to use force.
Obama also linked U.S. involvement in Iraq to Iran's increasing regional influence, saying the war had strengthened Tehran's hand in the Middle East.
"Because of the war in Iraq, Iran, which always posed a greater threat to Israel than Iraq, is emboldened and poses the greatest strategic challenge to the United States and Israel in a generation," Obama said. "Iraq is unstable, and Al-Qaeda has stepped up its recruitment. Israel's quest for peace with its neighbors has stalled despite the heavy burdens borne by the Israeli people, and America is more isolated in the region, reducing our strength and jeopardizing Israel's safety."
For that reason, he said, as president he would begin to withdraw U.S. troops from Iraq and thus signal to Iran that the U.S. military is not "tied down."
"Keeping all of our troops tied down indefinitely in Iraq is not the way to weaken Iran. It is precisely what has strengthened it. It is a policy for staying, not a policy for victory," Obama said. "I have proposed a responsible, phased redeployment of our troops from Iraq. We will get out as carefully as we were careless getting in. We will finally pressure Iraq's leaders to take meaningful responsibility for their own future."
On the issue of the Israeli-Palestinian conflict, Obama said he favors the creation of a Palestinian state that will afford Palestinians a chance to thrive, but said any agreement must preserve Israel's identity and keep Jerusalem as the undivided capital.