Israel supporters expect Biden to deliver reassurances on Iran policy at AIPAC

When Vice President Joe BidenJoe BidenBiden reveals .45 billion loan to Amtrak Trump was wrong: Kaine is a liberal in a moderate's clothing Trump poised to betray primary supporters on immigration MORE addresses the main pro-Israel lobby on Monday, he'll be expected to deliver some tough talk on Iran, following repeated attacks against the administration's trustworthiness.

President Obama has repeatedly vowed to prevent Iran from gaining a nuclear weapon. But recent events – the bruising 2012 election, the bitter fight over Chuck HagelChuck HagelThere's still time for another third-party option Hagel says NATO deployment could spark a new Cold War with Russia Overnight Defense: House panel unveils 5B defense spending bill MORE's nomination, a new proposed deal with Iran – have raised concerns among some Israel supporters.

Less than a month before Obama's first official visit to Israel, Biden has been chosen to put any lingering concerns to rest. The three-day conference of the American Israel Public Affairs Committee, an annual opportunity for top U.S. and Israeli leaders to show a united front before 13,000 activists, is seen as the ideal venue.

“Vice President Biden will make clear that the support for Israel, and the U.S.-Israeli relationship, and the goal of preventing Iran from gaining a nuclear weapon, is shared by both parties,” said Aaron Keyak, the executive director of the National Jewish Democratic Council.

“What we'll see at AIPAC Policy Conference is despite all of the partisanship, the growing divide between Republicans and Democrats on almost every issue, both parties are going to come together in support of this one issue,” Keyak said.

Josh Block, CEO and president of the Israel Project, said Biden's speech isn't aimed so much at reassuring pro-Israel Americans as it is about sending a clear signal to the rest of the world.

“It's a question of articulating so that the Iranians and others believe – and hear, again and again – that we are absolutely serious when we say that we're not going to let them get to breakout capacity, as the president has said,” Block said.

“And every opportunity to articulate that point in a high profile place is a valuable opportunity … because of the critical importance of the substance of the message being delivered not to ears in the room, but to ears in Tehran.”

He said the AIPAC audience was well informed of the debate around Iran.

“There have been points in which the administration tried to calibrate these sanctions in ways which moved slowed than some in Capitol Hill and in other places [would have preferred],” he said. “So articulating again in a very thorough and specific way the administration's views on this is certainly something that people would be glad to hear.”

Biden's office had no comment.

Obama addressed the group in person last year, as he did in 2008 and 2011. Biden spoke in 2009, and Secretary of State Hillary ClintonHillary Rodham ClintonNavarro on Trump: 'He's unfit to be human' Ice Cube: 'I will never endorse a mothaf---a' like Trump Would internet transition have an impact on current US election? MORE in 2010.

“I have said that when it comes to preventing Iran from obtaining a nuclear weapon, I will take no options off the table, and I mean what I say,” Obama said last year. “That includes all elements of American power: A political effort aimed at isolating Iran; a diplomatic effort to sustain our coalition and ensure that the Iranian program is monitored; an economic effort that imposes crippling sanctions; and, yes, a military effort to be prepared for any contingency.”

Those words didn't stop Republicans from repeatedly questioning his commitment during the presidential election.

“Look, one thing you can know and that is if we reelect Barack ObamaBarack ObamaDems' Florida Senate primary nears its bitter end Former Obama campaign manager diagnoses Trump on air as 'psychopath' Pence: Dems' racism accusations 'sound desperate' MORE, Iran will have a nuclear weapon,” Republican candidate Mitt Romney said last year. “And if we elect Mitt Romney, if you elect me as the next president, they will not have a nuclear weapon.”

The issue gained renewed traction during the confirmation hearing for Secretary of Defense Chuck Hagel. Like Obama's pick for secretary of State, John KerryJohn KerryClinton faces decision in Trump attack strategy Watchdogs warn of 'serious' conflicts of interest for Clinton Foundation Kerry: More 'work to do' in avoiding civilian casualties in Yemen MORE, Hagel is a combat veteran who is seen as particularly wary of going to war – with an added history of controversial comments about Israeli influence on U.S. foreign policy and a preference for negotiating with Israeli foes like Iran and Hamas.

Hagel's first meeting with a foreign counterpart will be with Israeli Defense Minister Ehud Barak, proof for Keyak that the military relationship with Israel remains as strong as ever.

This week's decision by the administration and its partners to soften their demands on Iran has also raised questions in some quarters. The six parties this week offered to let Iran keep open a secretive uranium enrichment plant as long as enrichment was suspended, and to keep a small amount of enriched uranium, which Iran says it needs for medical research.

Sen. Marco RubioMarco RubioDems' Florida Senate primary nears its bitter end Would internet transition have an impact on current US election? Conway: Trump will take a look at deportation policy MORE (R-Fla.), a potential Republican front-runner in 2016, said Israeli leaders made it abundantly clear to him during his trip to Israel last week that they think the Iranians are just playing for time.

Israel “has a number of issues they're very concerned about. At the top of the list is Iran,” Rubio said at a policy forum at the pro-Israel Washington Institute for Near East Policy on Wednesday. “I think – and I'm not saying anything they're not saying publicly – I think they are convinced that Iran is going to move forward for a weapons program, or the capacity for weapons, and that they're using negotiations as a ploy to buy time, but that ultimately no amount of economic sanctions … is going to stop Iran from moving forward with its weapons program.”

He urged Obama to use his trip to reassure Israel that “we are firmly committed to the security of our allies.”

“I think, from what I've read and seen, that that is largely the message that the president will take to the region,” he said. “And, if he does, then that's a positive thing.”