Can Israel convince West to stay sceptical over Iran?
When the Israeli Prime Minister, Benjamin Netanyahu, addressed the UN General Assembly last year he took with him a prop - a cartoon graphic of the Israeli view of Iran's progress towards making a nuclear weapon.
The information was contained on a picture of a large circular bomb of the sort anarchists used to carry in cartoons, complete with a fizzing fuse.
This year, as the diplomatic atmosphere around him changes, the occasion calls for more subtle tactics.
Israel has watched with obvious discomfort as Iran's efforts to remake its image in the eyes of the Western world have been welcomed by the United States and its allies.
All President Hassan Rouhani had to do to be a success at the UN was not be his predecessor Mahmoud Ahmadinejad.
So, mission accomplished.
Gone was the strident, hostile (and predictable) tone of the Ahmadinejad era.
In its place there was an easiness of manner and an openness to engagement which the West was eager - Israel might say desperate - to embrace.
One Israeli official has called it an Iranian charm offensive - there have even been stories that Mr Rouhani is thinking aloud about restoring direct flights between Iran and the United States, which stopped after the Islamic Revolution swept away the Shah in 1979.
As Mr Netanyahu left Israel for the United States he summed up his mission in these terms.
"I will tell the truth," he said, "In the face of the sweet-talk and the onslaught of smiles. One must talk facts and one must tell the truth."
Israel's problem is simple. Its perception of Iran and the threat it poses has not changed at a moment when it looks like everybody else's perception might be changing.
There is a danger that Mr Netanyahu might sound like he is singing the same old song at a moment when the rest of the world hopes it is detecting new mood music in Tehran.
The view in Israel is that a new front-man for the Iranian regime - and a new tone - should not mean that years of belligerent rhetoric are forgotten. Plenty of Israelis are worried that an Iranian nuclear weapon would be an existential threat to the Jewish state.
It wants the sanctions regime which is crippling the Iranian economy to be stringently applied and backed up with a credible military threat.
There is a widespread assumption in the Middle East that if Israel judged that Iran had passed the point of no return on the creation of a bomb and could not persuade the US to take military action that it would do so itself.
Israel's critics and enemies would question its right to launch such an attack - not least because they, like everyone else, believe that Israel itself already has nuclear weapons.
Its policy of "nuclear ambiguity" - essentially declining to comment one way or the other on the issue - does not cut much ice in the Arab world or with Iran.
Israel's nightmare is that the rest of the world may be taken in by what might amount to nothing more than an Iranian delaying tactic.
Under the guise of holding talks, this argument goes, Iran could keep working on its nuclear programme until its levels of expertise and stockpiles of enriched uranium have reached points of no return. It might even seek the reward of a relaxation in sanctions for agreeing to the talks.
There are those in leadership circles in Israel who see parallels between the evolution of Iran's nuclear programme and the rise of Hitler in the Europe of the 1930s.
The world once again faces a choice between appeasing a threat and confronting it - and Israel is worried that Barack Obama might ultimately make what it regards as the wrong choice.
Israel is not alone in the Middle East in watching the signs of change in Tehran with some anxiety.
As the leader of the Sunni Islamic world, Saudi Arabia is fighting a vicious proxy war with Shia Iran in Syria - the Saudis and some of their Gulf allies fund the opposition including many Jihadist groups.
Iran props up the Assad regime and uses its South Lebanese militia Hezbollah for much of the frontline fighting there.
The Iranian government has been prepared to spend blood and treasure in Syria even while its economy is creaking under sanctions.
It might be able to do more if the West were to agree to lift those sanctions in the hope of encouraging a new political atmosphere in Iran.
So Israel's mission is a difficult one - not the kind of thing you can illustrate in cartoon graphic to accompany a set-piece speech on the world stage.
Mr Netanyahu's government cannot afford to look out of step with the United States - its strategic partnership with the Americans is still its most important diplomatic asset.
But its most important friend is reaching out to its most dangerous enemy and for the moment at least Israel is still searching for a convincing answer.