JERUSALEM » Michael B. Oren, who spent four years as Prime Minister Benjamin Netanyahu’s ambassador to Washington, has called on Netanyahu to cancel his speech to Congress about Iran. Amos Yadlin, a former military intelligence chief who frequently briefed the Israeli prime minister on security matters, denounced the event as "irresponsible."

Both men criticized their former boss for politicizing issues vital to Israel’s future. Both also have their own political motives: Oren is running for Parliament with a new center-right party, and Yadlin is the defense-minister designee of the center-left party Zionist Camp.

If Netanyahu imagined that the speech, scheduled for two weeks before the March 17 elections in Israel, would bolster his status as statesman, the undiplomatic way it was arranged has instead given his challengers an opening to undermine his main campaign platform. The backlash, not only from the White House but also from congressional Democrats, has reverberated in Israel, where maintaining bipartisan support in Congress is considered as crucial as preventing Iran from developing nuclear weapons.

On Tuesday Senate Democrats who had been pushing a new sanctions bill against Iran — which Netanyahu supports — said they would hold off a vote until late March, handing the Obama administration a victory.

As in the United States, conservatives like Netanyahu tend to have the advantage when election campaigns are about security, and so far his opponents have emphasized pocketbook issues and corruption. But political analysts say that international isolation is a prime public concern of Israelis, and that attacking Netanyahu for deteriorating relations with Washington, Israel’s main defender on the world stage, could be a winning message in a tightening race.

"It’s a huge miscalculation," said Eytan Gilboa, a professor at Bar Ilan University who specializes in political communication and Israeli-American relations. "People are now questioning his judgment. If the opposition would not just focus on economic and social issues, but also argue against his claims on security and foreign policy, I think this exercise might backfire."

The invitation to address a joint meeting of Congress to make the case for new sanctions on Iran came from the House speaker, John A. Boehner, a Republican. Boehner did not consult either the Obama administration or his Democratic counterparts, something several veteran diplomats described as unprecedented. The White House responded with its own snub, announcing that President Barack Obama, who has promised to veto any new sanctions, would not meet with Netanyahu while he was in town.

While officials on both sides say the underlying security and intelligence cooperation between the United States and Israel will continue, some political analysts close to the Obama administration say it may not work as hard to rally its allies to Israel’s side in critical forums like the United Nations.

Netanyahu, who has made the Iranian nuclear program a mainstay of his career, insists his motivations are not political and declared on Sunday: "I will go anywhere I am invited in order to enunciate the state of Israel’s position and in order to defend its future and its existence." Ron Dermer, the Israeli ambassador to Washington who orchestrated the invitation with Boehner, said at an event in Florida that speaking out on Iran was the prime minister’s "deepest moral obligation" and "most sacred duty."

Yaakov Amidror, Netanyahu’s former national security adviser, said that "about the issue of Iran he is willing to go very far."

"He is ready to do everything to prevent it from being signed, what he thinks is a bad agreement, to risk many things," Amidror said of Netanyahu. "It is only because from his point of view he should prevent something that is so critical to be materialized that he allows himself to make moves that otherwise he would not."

Experts on Iran said they did not see any new developments in the continuing nuclear negotiations, or in the differences between Obama and Netanyahu, that might explain the timing of the speech, or what appeared to be the willingness to risk the repercussions of its unorthodox arrangement. Some critics of the prime minister fear that the whole episode is strengthening Iran’s hand.

Israeli and American commentators have described a toxic mix of political considerations in both countries — a touch of pre-election panic by Netanyahu meeting up with Boehner’s opportunism. Many have called it self-promotion with a high cost, clumsy at best, if not cynical.

"It’s proven again that what we export best as Israelis is chutzpah," said Mitchell Barak, a Jerusalem political consultant and pollster. Nahum Barnea, a leading Israeli columnist, said Netanyahu "lost the major benefit" of the speech because "the whole idea is now contaminated."

David Makovsky of the Washington Institute for Near East Policy said that "unless Netanyahu changes the date it’s hard to escape the view that this was deliberate."

"If it’s really all about Iran, then make it all about Iran," said Makovsky, who worked for Secretary of State John Kerry on the Israeli-Palestinian peace talks that collapsed last spring. "I understand why he wants to make his case, but let him do it after the Israeli elections. Iran and bipartisan U.S.-Israel ties are too vital to be politicized."

Netanyahu, whose relationship with Obama has been rocky from the start, was also accused of meddling in the 2012 presidential campaign by embracing the Republican challenger, Mitt Romney, in Jerusalem. The appointment of Dermer, who grew up in Florida and once worked for a Republican pollster, has hardly helped.

With Israeli polls showing Netanyahu’s Likud Party and the Zionist Camp running about even, candidates were quick to make hay of the congressional controversy, which dominated headlines here for four days.

Isaac Herzog, the leading challenger for the premiership, said on Army Radio, "What Netanyahu is doing with this violent behavior is to harm the security interests of Israel." Herzog’s partner in the Zionist Camp, Tzipi Livni — a former foreign minister who has made her relationships with foreign leaders a prime campaign point — called the speech "gravely irresponsible."

Yair Lapid of Yesh Atid, a centrist faction focused mainly on economic issues, warned, "This damage will take a long time to mend."

Yehuda Ben Meir, an expert on public opinion at the Institute for National Security Studies in Tel Aviv, said surveys had consistently shown that Israelis see a decrease in American support and a nuclear-armed Iran "as the two most serious threats, almost equal in severity." Israelis are highly critical of Obama, and may appreciate Netanyahu’s standing up to him, but losing congressional Democrats, Ben Meir said, would play differently.

"Most people in Israel feel or think or believe that mainly this was done for internal political reasons," Ben Meir said. "His base may say he went because of the Iranian issue, but those swing voters — and what’s important is always the swing vote — it could among certain parts of the electorate harm him. It might be that he didn’t properly estimate the fallout."

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