"I had 700 days of 'no' in Northern Ireland, and one 'yes'," remarked George Mitchell in May 2010. A year on, and having spent more than 800 days in the Middle East with no sign of a "yes" on the horizon in Ramallah or Tel Aviv, the frustrated former senator announced his resignation as President Obama's peace envoy to the region.

Cue much hand-wringing about the future of the "peace process". But there is nothing new about the Obama administration's failure to get Israelis and Palestinians back to the negotiating table; peace talks have been on hold since 2008. As the mild-mannered Palestinian president, Mahmoud Abbas, a long-time ally of the US, noted in a recent interview: "It was Obama who suggested a full settlement freeze. I said OK, I accept. We both went up the tree. After that, he came down with a ladder and he removed the ladder and said to me, jump."

Obama, however, like George W Bush before him, is a distraction. When it comes to the US's Middle East policy, true power and influence lies elsewhere. Pronouncements from the executive branch of the US government attract much of the attention of foreign governments and the world's media; few outside (or, for that matter, inside) the US pay attention to the behaviour of the country's legislature when it comes to Israel and the Palestinians.

It is Congress that passes resolution after resolution backing Israel and condemning the Palestinians; it is Congress that approves arms sales to Israel and grants Tel Aviv billions of dollars in aid. Presidents, secretaries of state and special envoys come and go; meanwhile, Congress, whether Republican- or Democrat-controlled, always stands four-square behind Israel's occupation of the West Bank.

Following the Aipac

The Congress of the United States consists of 100 senators and 435 members of the House of Representatives; in effect, just 535 Americans are blocking efforts to bring peace to the Middle East. Why? Forget the pious guff about Israel being the region's "only democracy" and a "valued friend and ally" of Washington. In the corrupt and dysfunctional US political system, where legislators are outnumbered by special interests, from the gun lobby to Big Pharma, the Israel lobby - specifically, the American Israel Public Affairs Committee (Aipac) that brags on its website about being "the most important organisation affecting America's relationship with Israel" - has a financial stranglehold on both main parties. According to William Quandt, a former adviser on the Middle East to the Nixon and Carter administrations, "70 per cent to 80 per cent of all members of Congress will go along with whatever they think Aipac wants".

It is Aipac that polices congressional votes on Israel, demands unconditional US support for the occupation of the West Bank and insists that Israel remain the largest single annual recipient of US foreign aid ($250 a year per Israeli, compared to $1 a year per African). Consider this: the upper and lower houses of Congress are more divided, polarised and partisan than in any other period in recent history. Democrats and Republicans agree on nothing. Except Israel.

Presidents who have tried to pressurise the Israelis - from Reagan to Obama - have found themselves attacked not just in the Knesset but in Congress. In the words of Paul Findley, a Republican from Illinois who served in the House of Representatives for 22 years before being
defeated by an Aipac-funded candidate in 1982: "Congress behaves as if it were a subcommittee of the Israeli parliament." The irony is that there is far more heated debate about Israel's actions on the floor of the Knesset than on Capitol Hill. "For 35 years, not a word has been expressed . . . in either chamber of Congress that deserves to be called debate on Middle East policy," Findley wrote in 2002.

A move to J Street

On 2 May 2002, after Ariel Sharon's invasion of the West Bank and the destruction of the Jenin refugee camp, both houses of Congress overwhelmingly approved resolutions expressing "solidarity with Israel" - 352 to 21 in the House, 94 to two in the Senate.

On 20 July 2006, eight days after the start of Israel's war against Lebanon, Congress passed a resolution endorsing Israeli military action by a vote of 410 to eight. On 9 January 2009, as the Palestinian death toll from the Israeli air assault on Gaza topped 700, the House of Representatives passed a resolution "reaffirming the United States' strong support for Israel in its battle with Hamas". The margin was 390 votes to five.

These comically one-sided resolutions illustrate the power and influence of the Israel lobby on Capitol Hill - and the way in which craven legislators in both main parties blindly throw their support behind any and every act of belligerence. As Uri Avnery, the Israeli author and peace activist, once remarked: if Aipac "were to table a resolution abolishing the Ten Commandments, 80 senators and 300 congressmen would sign it at once".

But, slowly, the tide might be turning: the left-leaning, liberal Jewish lobby group J Street, founded in 2008, now provides political and
financial support to about 50 members of Congress and aspires to become a counterweight to the hawks at Aipac. And on 22 May, pro-peace groups will hold a "Move Over, Aipac" rally in Washington, DC to try to remind legislators down the road at Aipac's annual policy conference not to conflate the views of the Israel lobby with US Jewry.

In September, the UN General Assembly will prepare for a vote on whether to recognise Palestine as a sovereign state. But Israel's illegal occupation of the West Bank is a reminder of just how irrelevant UN votes are. It is the votes on Capitol Hill that matter.