Despite the money advantage, AIPAC doesn't have the political numbers on their side. Obama has said he'll veto any attempt by Congress to kill the deal, which means the House and Senate will each need a 2/3 majority to override. That's why it's critically important that you let your electeds know you support the Iran deal:

As the Senate opens a two-month congressional review of the nuclear agreement with Iran on Thursday, opponents of the deal are spending tens of millions of dollars to rally the American public and U.S. lawmakers against it.The American Israel Public Affairs Committee(AIPAC), Citizens for a Nuclear Free Iran, United Against a Nuclear Iran and the Republican Jewish Coalition are among groups that will spend between $20 million and $40 million to blast the deal with TV commercials that began airing last Friday, social media ads and new websites that include alleged flaws in the agreement and contact information for members of Congress.

The opponents' effort dwarfs that of supporters. The liberal Jewish group J Street has raised $2 million to promote the deal, said spokesman Alan Elsner. Other liberal groups, such as MoveOn.org, are also mobilizing supporters in favor of the deal, though it's unclear how much money they've raised. And President Obama is using the White House bully pulpit to make his pitch to the American people in support of the accord, which limits Iran's nuclear program for 15 years in return for lifting economic sanctions.

Obama is sending three members of his Cabinet — Secretary of State John Kerry, Energy Secretary Ernest Moniz and Treasury Secretary Jack Lew — to defend the deal at Thursday's hearing. Republicans, who hold a majority in the Senate, have been vocal critics of the accord, saying it doesn't provide ironclad guarantees that Iran won't build a nuclear weapon secretly.