However, in recent years the role on Capitol Hill of aggressive Israeli lobby groups, such as the American Israel Public Affairs Committee (Aipac), has come under scrutiny.

Famously, columnist Thomas Friedman referred in The New York Times to Congress' multiple standing ovations for a 2011 speech by Netanyahu "as bought and paid for by the Israel lobby".

In recent days, committees of both the House of Representatives and the Senate have unanimously voted for controversial Aipac-backed amendments that would penalise states and organisations if they support boycott, divestment or sanctions (BDS) campaigns against either Israel or its illegal settlements in Palestinian territory.

If the legislation passes, it would appear to be "the first-ever formal step toward US government recognition of the settlements' legitimacy", according to an op-ed in Jewish daily The Forward.

Adelson's deep pockets

Attention is now turning to the impact of wealthy American Jewish donors on the 2016 presidential race. Indications are that they will seek to ensure that the candidates are as supportive of Israel - if not Netanyahu himself - as the Congress.

The man with the deepest pockets is widely expected to be 81-year-old Adelson, whose wealth is estimated at $40 billion. He reportedly sank $150 million into the unsuccessful Republican bids by Newt Gingrich and Mitt Romney in the 2012 race.

Adelson is known for his ultra-hawkish positions on Israel and his intimate ties to Netanyahu. Like the Israeli prime minister, he is deeply opposed to a two-state solution, preferring that the Palestinians remain stateless.

Last year he donated $25 million to Ariel university, located in a Jewish settlement deep in the occupied West Bank.

He has said "the Palestinians are an invented people", and that their chief goal is "to destroy Israel".

Last November at a conference in Washington he dismissed the idea of a Palestinian state, even if it meant that the resulting "Greater Israel" disenfranchised a Palestinian majority: "I don’t think the Bible says anything about democracy… Israel isn't going to be a democratic state - so what?"

To circumvent strict political financing laws in Israel, Adelson created a free-sheet national daily, Israel Hayom, eight years ago. It is widely referred to as "Bibiton" - a play on Netanyahu's nickname and the Hebrew word for newspaper. It quickly became the highest-circulation newspaper in the country.

Netanyahu's coalition partners have called the paper Israel's version of Pravda. Israeli analyst Anshel Pfeffer has described its role as "slavishly pushing [Netanyahu's] policies and defending him and his family from criticism".

While losing Adelson an estimated $5 million a year, Hayom has left the largest paid-for newspaper, Yedioth Aharanoth, which is critical of Netanyahu, struggling both for readers and advertising revenue.

Last November, a bill to curtail Hayom's influence comfortably passed its first reading in the Israeli parliament, days before Netanyahu called an unexpected election. There has been widespread speculation that Adelson insisted on an early election, half-way into Netanyahu's term, to forestall any danger of the bill becoming law.

Ideological soul-mates

But, while Netanyahu has faced diminishing impediments to advancing his right-wing agenda at home, he has found himself repeatedly at odds with the White House during Obama's term.

Adelson appears keen to remedy that by ensuring that Netanyahu has an ideological soul-mate in the White House after the 2016 US election.

Thomas Friedman wrote in The New York Times in March that Adelson's goal was to "simultaneously push Israel and America toward eliminating any two-state solution between Israelis and Palestinians, toward defunding the Palestinian Authority and toward a confrontation with Iran".

Last year, Republican front-runners for the presidential nomination were summoned to one of Adelson's Las Vegas hotels for a conference organised by the Republican Jewish Coalition - and for personal questioning by Adelson on their views about Israel.

The conference, repeated this month, has been widely described as the "Adelson primaries".

In an indication of the high stakes for potential candidates of losing Adelson's support, New Jersey governor Chris Christie hurried to apologise to the billionaire after referring - correctly - during last year's event to the "occupied territories".

Christie reportedly regained Adelson's favour after saying he had misspoken and that he was a true friend of Israel.

Even Adelson's preferred choice for the 2012 race, Newt Gingrich, has warned that donors like Adelson have too much sway, arguing that the election process "radically favours billionaires".

Other contenders appear equally aware of the pressures. Last week Senator Lindsey Graham joked of his efforts to raise funding that he might end up with "the first all-Jewish cabinet in America". He concluded: "Bottom line is, I've got a lot of support from pro-Israel funding."

Other hawkish donors

Adelson is not the only Jewish donor with hawkish views about Israel who is putting money into the Republican campaign. Last month the Jewish Telegraphic Agency ran an assessment of each leading contender - and what it termed "His Jews", referring to Jewish donors.

The most important after Adelson is likely to be Norman Braman, an 82-year-old car dealership tycoon. He is reported to be preparing to spend $25 million on his preferred choice - currently, Florida Senator Marco Rubio.

In interviews, Braman has been outspoken in support of an aggressive Israel: "How do you make peace with people [Palestinians] who want to destroy you and are dedicated to your destruction?"

He also argued that the idea of the Jews as "weak" changed with Israel's creation. "All the advantages that Jews have today, that generations have since the establishment of Israel, have been augmented by Israel."

After entering the Senate, Rubio made his first trip to Israel to meet Braman and family members there, and has since frequently spoken of his love for Israel. In March, as he criticised Obama for falling out with Netanyahu, Rubio said Israel had a "unique purpose" and described it as "everything we want that region of the world to be".

Rubio was reported last month to be Adelson's preferred candidate for the nomination too.

'No right or left on Israel'

Meanwhile, the strongest Democratic challenger, Hillary Clinton, who announced her candidacy last month, is likely also to be under pressure to show her unequivocal support for Israel.

Her chief backer is Haim Saban, an Israeli-American media mogul who is a long-time friend of the Clinton family, a major Democratic Party donor and an ardent supporter of Israel.

He has said he will spend "whatever it takes" to get Clinton elected president, and that under her leadership "I believe - deeply - the relationship with the US and Israel will be significantly reinforced". He added that "there's no right or left when it comes to Israel".

Saban is supportive of negotiations over a two-state solution, but chiefly to protect Israel from a demographic takeover of Palestinians inside what would become a Greater Israel. "It is not about granting the Palestinian state," he has said. "It's about securing the future of a democratic Israel."

Meanwhile, Saban has echoed Netanyahu's hardline positions on Iran.

Last November, at a meeting of Israeli-Americans also attended by Adelson, Saban attacked Obama for negotiating with Iran. He said, if he were Netanyahu, he "would bomb the living daylights out of these sons of bitches [Iran]" and that the US had "shown too many carrots and a very small stick".

Saban spoke of his dissatisfaction with Obama's attitude to Israel even before he became president. Journalist Avner Hopstein revealed in the Israeli daily Haaretz last month that in an interview in late 2008, shortly before Obama assumed office, Saban had confided that he was "very worried" about the new president.

According to Hopstein, Saban feared that Obama would impose new standards of conduct on Israel in its dealings with the US and make demands "diametrically opposed to that of his predecessors".

Battle of the philanthropists

A battle between "two pro-Israel philanthropists", concluded Hopstein, would create a campaign in which Clinton would have to prove that she is "better for the Jews, for Israel and perhaps even for Netanyahu".

That process already appears to be underway. Shortly before Clinton's announcement of her presidential run, she met Malcolm Hoenlein, head of the Conference of Presidents of Major Jewish Organizations.

In a press statement afterwards, apparently intended to distance Clinton from Obama's clashes with Netanyahu, Hoenlein said Clinton "thinks we need to all work together to return the special US-Israel relationship to constructive footing".

It is almost certain that the campaign runs of both the Republican and Democratic presidential candidates in 2016 will depend on financing from hawkish, pro-Israel donors such as Adelson and Saban.

A concern for a growing number of Americans, as their candidates seek to win over such patrons, must be: can a US president and Congress still afford to pursue foreign policy goals separate from those of Israel?

Jonathan Cook is a veteran journalist based in Nazareth.