Prime Minister Benjamin Netanyahu’s upcoming address to a joint meeting of Congress will probably be the most important speech of his career — and one that has already jeopardized relations between Israel and the United States.

On Tuesday morning, Netanyahu will confront an American president and insist that the future of the State of Israel, and the world, is imperiled by a pending “bad deal” with Iran on its nuclear program.

Also hanging in the balance is Netanyahu’s own political future. Just two weeks after the speech, Netanyahu will either be reelected to a historic fourth term as prime minister or be out of a job.

Netanyahu has spent three terms as Israeli prime minister focused on the dangers posed by Iran. In his first address to Congress in 1996, he warned that an atomic Iran would “presage catastrophic consequences, not only for my country, and not only for the Middle East, but for all mankind.”

His supporters call him prescient; his detractors say Netanyahu has been warning for 20 years that “time is running out” on the Iran threat. His critics say Netanyahu is a broken record, a Cassandra obsessed, willing to deeply damage U.S.-Israeli relations in a futile confrontation with the United States that wins Israel nothing.

Comparing terms of Israeli prime ministers

His opponents in Israel and the United States say the speech is mostly a cynical ploy to get reelected in a tight March 17 vote, by fear-mongering on Iran and by opposing an American president who is not very popular in Israel.

On Tuesday morning, as Secretary of State John F. Kerry meets with his counterparts in Switzerland to try to complete a framework accord with Iran by the end of March, Netanyahu will stand at the lectern in Congress to tell Americans, essentially, that President Obama is either foolhardy or weak and about to sign a deal with the devil.

Netanyahu will warn, as he has in the past, that the Americans are gambling on a radical Iranian regime run by Muslim clerics who deny the Holocaust, sponsor terrorist groups, support a murderous regime in Syria and pledge to destroy Israel.

As his chartered plane wings toward Washington on Sunday afternoon, Netanyahu’s advisers say the final author of the speech will be Netanyahu himself.

The prime minister’s press office released photographs of Netanyahu penning his speech in longhand.

Netanyahu will write the speech because he considers himself not only an authority on the minutiae of the Iran nuclear program — the number, type and productivity of the centrifuges and the estimates of low-enriched uranium to the kilogram — but also an expert on U.S. politics and the American people.

Netanyahu studied at MIT and served as Israeli ambassador to the United Nations in New York. He has been called the “most American” of Israeli prime ministers.

This is his moment. Netanyahu’s English is fluid, conversational, persuasive and often blunt. He has a flair for stagecraft. His guiding light, says his inner circle, is Britain’s wartime premier and great orator, Winston Churchill, who is the only other foreign leader to have addressed a joint meeting of Congress three times.

During Netanyahu’s second speech to Congress in May 2009, he received 29 standing ovations.

Netanyahu’s critics in Israel and in the Obama administration warn that the Israeli leader is really no Churchill and that he has seriously miscalculated this time.

Israeli relations with Democrats and the Obama administration are at a historic low.

A top Israeli diplomat said that Netanyahu, if reelected, has already written off his relations with Obama in his last two years in the White House, a potentially perilous gambit for a Middle East leader surrounded by enemies.

National security adviser Susan E. Rice on Tuesday denounced the upcoming address as “destructive” to the relationship between the United States and Israel.

A senior U.S. official said Friday that the strategy is to stand aside and let Netanyahu give his speech, which will neither derail Iran talks nor sway Congress to block a possible agreement.

The senior official, who agreed to present administration views in exchange for anonymity, said the speech is more about Netanyahu’s reelection bid and his preoccupation with Iran — a clear and present threat shared by the Obama White House, but approached in a more pragmatic manner.

“The Netanyahu myth is that he alone understands the Americans,” said Alon Pinkas, a former Israeli consul general in New York and former adviser to four Israeli foreign ministers.

Pinkas said the speech will be applauded by Republicans but will do little to shape the Iran deal. “He is a grumpy, old man. He’s like a Republican senator from West Jerusalem. He talks like them, he dresses like them. He is always saying, ‘They’re against me! They don’t like me!’ He’s dealing with an America he doesn’t know.” Pinkas predicted the speech will fall flat.

Israeli journalist and author of the best-selling history “My Promised Land,” Ari Shavit, said he expects Netanyahu to give “a brilliant and desperate speech.”

Shavit is sympathetic. He sees the Iranian threat as more “bloodcurdling” than ever. Yet he says the prime minister has made a mistake by working against the U.S. administration rather than beside it.

Now “Israel rather than Iran has been isolated,” Shavit wrote in a recent column .

Netanyahu has opposed any deal with Iran that does not dismantle its uranium-enrichment program and insisted that economic sanctions should be stiffened, not lifted. Kerry and his negotiators have said such a deal is impossible.

Senior administration officials say an imperfect agreement that freezes Iran’s nuclear ambitions and allows for monitoring leaves the world in a much safer place than a rogue Iran with the potential to rush toward a bomb in clandestine bunkers packed with centrifuges.

Iran has long maintained that it seeks only a peaceful atom, and it is within its rights to research and exploit nuclear energy.

Netanyahu does not believe this. The Israeli leader has brushed aside appeals by Jewish leaders in the United States, congressional Democrats and some of his allies at home to pull back and find a face-saving way to cancel the speech.

In Israel, Netanyahu faces an extremely tight race for reelection against a surprisingly strong challenger, Isaac Herzog, leader of the Labor Party, who has pounded Netanyahu for endangering U.S.-Israeli relations with his speech.

Two hundred former generals and commanders of the Israeli Defense Forces, Mossad intelligence agency, Shin Bet domestic security and National Police are scheduled to appear at a joint news conference Sunday to urge Netanyahu to avoid any further deterioration of the U.S.-Israeli strategic relationship.

All this may help Netanyahu at home. “There will be nothing new in this speech,” said Dan Avnon, a lecturer of political theory at Hebrew University in Jerusalem. “The question here is who will be able to replace him? Can anyone else stand up in Congress and talk so forcefully against the leader of the United States? This has an effect on voters in Israel. People sit at home and say this man really steps up to the pressure.”

“What will happen after the speech? I honestly don’t know,” said Yuval Steinitz, Israeli minister of intelligence and strategic affairs, a Netanyahu confidant and the Israeli government’s top authority on the nuclear talks.

“It will be very clear this is a historic speech,” Steinitz said. “Because this issue is burning in his bones. He really feels that as prime minister of Israel this is his first priority, above all other issues.”

Netanyahu’s speech is going to be especially challenging, as it must reach multiple audiences with multiple messages.

“He is speaking to the people of Israel, his political system, to the administration, to Congress and to the American people, as well,” said Dore Gold, president of the Jerusalem Center for Public Affairs and a former foreign policy adviser to the prime minister who is still part of his inner circle.

“I think the notion that this speech is for political purposes is baseless,” said Gold, a former Israeli ambassador to the United Nations.

Netanyahu has reveled on the grand stages afforded him in past performances at the United Nations and before Congress. In a September 2012 address before the U.N. General Assembly, Netanyahu employed a kind of Wile E. Coyote drawing of a bomb with a fuse and took out a marker to draw a literal red line.

Netanyahu’s intelligence minister said he has not seen a draft of the speech, but he said the prime minister will stress that leaving Iran with thousands of centrifuges and a stockpile of uranium — materials that Israelis say would allow Iran to break through to a nuclear bomb in months, not years — is too dangerous.

“Our position is simple,” Steinitz said. “Iran built a nuclear program in secret, illegally. They want normal relations with the world? Okay, dismantle it.”

Ruth Eglash and Anne Gearan contributed to this report.