WASHINGTON – Legions of Israel’s most active supporters descended on Washington this weekend for the annual policy conference of AIPAC, the US’s largest pro-Israel lobby.

The conference, which begins on Sunday night and is to run through Tuesday, has become a Washington ritual: US policy-makers and journalists pause to focus, size up and tailor America’s broad alliance with Israel, their shared challenges across the Middle East and what, if anything, has changed since last year’s checkup.

The answer to that question looks to be more stark than it has been in previous years. At last year’s conference, Mahmoud Ahmadinejad was still president of Iran and the Middle East peace process was nowhere to be found on the Obama administration’s agenda.

Since then, the renewal of US diplomatic efforts on both fronts and the further deterioration of the conflict in Syria has muddled the America-Israel Public Affairs Committee’s message on Capitol Hill, where its influence is greatest.

Throughout the fall, AIPAC lobbied aggressively for a bill that would trigger new sanctions tools against Iran in the event negotiations fail to achieve a comprehensive solution to the nuclear crisis.

Their efforts resulted in broad public support for the bill, formally known as the Nuclear Weapon Free Iran Act of 2013. But in his State of the Union address in January, US President Barack Obama threatened to veto it, warning its passage would undermine unity among international powers at the negotiating table.

Democratic support for a swift vote on the measure began to wane, forcing a rare retreat by the lobby.

AIPAC’s leadership is likely to push back against that notion this week, arguing that the bill is still alive and relevant as a force pressuring the parties to reach a “good deal” in Vienna over the next four months of talks.

According to Prime Minister Binyamin Netanyahu, more pressure would be required to reach a settlement amenable to the Israeli government.

Headlining the first evening of the event is scheduled to be US Treasury Secretary Jack Lew, who is expected to discuss the implementation of sanctions on Iran through the duration of an interim deal.

US Secretary of State John Kerry and Netanyahu will also address the conference. In addition, Netanyahu is set to visit the White House for an Oval Office meeting with Obama and his chief aides.

AIPAC expects a forceful speech from Kerry in favor of peace between Israel and the Palestinians – less of a priority to AIPAC’s followers than the challenge of a nuclear Iran. In private, AIPAC officials say Kerry has accomplished “more in the past five months” on the peace process “than anyone has accomplished in five years.”

But while its leadership does not doubt Kerry’s commitment, their skepticism has not waned on his ability to bring the two sides to agreement on a final peace accord.

Some 14,000 people are expected to attend this year’s conference – a record number.

The organization says this year will be the most “diverse” gathering in its history.

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