The American-Israeli Public Affairs Committee (AIPAC), the most powerful pro-Israel lobby in the US, is holding its biggest annual conference yet with around 13,000 delegates in Washington.
Demonstrators from the occupy movement held a small protest outside the event urging no war on Iran and no US tax dollars for Israel.
On Sunday, Barack Obama, the US president, took to the stage and told the audience that Israel had never had a better friend in the White House. But he did not support Israeli military action against Iran's nuclear facilities - at least not yet.
Rick Santorum flew in especially for the event before heading back to Ohio, while Mitt Romney and Newt Gingrich appeared via satellite link.