The US’s largest pro-Israel lobby group is backing dozens of racists, homophobes and election deniers running for Congress next month because they have pledged to defend Israel against stiffening criticism of its oppression of the Palestinians.

The powerful American Israel Public Affairs Committee (Aipac) has justified endorsing Republicans with extremist views, including members of Congress with ties to white supremacist groups and representatives who attempted to block Joe Biden’s election victory, on the grounds that the singular issue of support for Israel trumps other considerations.

But Aipac’s support for rightwing politicians has privately embarrassed some Democrats also endorsed by the powerful group and drawn accusations from more moderate pro-Israel organisations that it is attempting to stifle legitimate criticism of hardline Israeli policies.

Logan Bayroff, a spokesman for J Street, a group campaigning for Washington to take a stronger stand to end the occupation of Palestinian territories, accused Aipac of attempting to impose a narrow definition of what it is to be pro-Israel amid shifting views in Democratic ranks.

“Their actions have made clear that they view pro-Israel, pro-peace progressive Democrats as threats – and Trumpist Republicans as allies. That worldview could not be more out of touch with the vast majority of American Jews,” he said.

“Aipac may hope to silence and intimidate political leaders who believe that settlement expansion, endless conflict and permanent occupation are harmful to Israel, the Palestinian people and US interests. Ultimately, however, these common-sense views are too popular, widespread and important to be suppressed, and will continue to gain strength within American politics and among the American Jewish community.”

Aipac’s backing of extreme rightwing Republicans follows its $27m advertising campaign during the Democratic primaries to defeat candidates who spoke up for Palestinian rights, mostly with attacks over issues that had nothing to do with Israel.

The campaign is part of push by more hawkish pro-Israel groups to shore up support in Congress in the face of rising advocacy for the Palestinian cause within the Democratic party and erosion of approval for Israeli actions among American Jews, particularly younger people.

Earlier this year, the Israeli foreign ministry director general, Alon Ushpiz, said protecting bipartisan support for the Jewish state in the US was at the top of a list of Israel’s diplomatic priorities amid wider government concern about the impact of a series of international human rights reports that it is practicing a form of apartheid over the Palestinians.

Among those candidates endorsed by Aipac is the New York congresswoman Elise Stefanik, a Trump loyalist whose home town newspaper criticised her for “despicable” advertising and “hateful rhetoric” that promoted the racist and antisemitic “great replacement theory”, claiming the US is being flooded with immigrants to outvote white people. The Times Union accused Stefanik of “fear-based political tactics”.

Another candidate backed by Aipac, the Pennsylvania congressman Scott Perry, pushed the same theory when he told a foreign affairs committee meeting “native-born” Americans are being replaced in order “to permanently transform the landscape of this very nation”.

Aipac has also endorsed other candidates who have associated with QAnon, the far-right conspiracy theory. Among them are the Georgia congressman Buddy Carter, who attended a QAnon-linked rally claiming links between Democrats and child sex rings, and a Florida congresswoman, Kat Cammack, who appeared on QAnon-related channels including Patriots’ Soapbox.

Other Republicans backed by Aipac have appeared on Patriots’ Soapbox. They include the Utah congressman Burgess Owens, who has promoted claims by the far-right conspiracy theorist Alex Jones and his Infowars website, including anti-migrant diatribes and false claims of election rigging. Owens distributed an Infowars article that smeared the bereaved Muslim father of a US soldier by pushing an unfounded suggestion that his legal work helped the 9/11 hijackers enter the US.

Aipac has endorsed Rick Allen, a Georgia congressman who refused to debate a fellow Republican at an Islamic community centre, calling it a “suspect venue”.

The hawkish lobby group is also backing candidates known for anti-LGBTQ+ views. They include Mark Green, a Tennessee congressman who once said “transgender is a disease”, as well as members of Congress who denounced the supreme court ruling making marriage equality a right.

Aipac’s approved list includes Steve Scalise, who opposed the end of anti-LGBTQ+ discrimination in the military, and Randy Weber, who broke down in tears as he begged God to forgive the US for the supreme court judgement.

“Father, oh Father, please forgive us,” he pleaded.

Aipac support for far-right and homophobic candidates flies in the face of its routine defence of Israel as a liberal democracy surrounded by authoritarian Arab regimes.

Pro-Israel groups routinely deflect criticism of what Israel’s leading human rights group, B’Tselem, called its “regime of Jewish supremacy” over Palestinians, systematic discrimination against Israel’s Arab citizens and the recent “nation-state” law that places Jewish identity over democracy, by emphasising Israel’s democratic credentials.

Aipac has consistently pushed the message that Israel is “the only LGBTQ+-friendly country in the Middle East”.

Last year, during one of Israel’s periodic assaults on Gaza that killed hundreds of Palestinians, the lobby group again resorted to what has become known as “pink washing” when it tweeted: “Do you support LGBTQ+ rights? Hamas doesn’t. Hamas discriminates against lesbian, gay, bisexual, transgender and intersex people.”

Aipac caused upset among its supporters earlier this year when it endorsed more than 100 Republican members of Congress who refused to certify Biden’s 2020 election victory. The list again includes Scott, who voted against awarding the Congressional Gold Medal to officers who defended the Capitol on January 6.

Richard Haass, a former US diplomat and president of the Council on Foreign Relations, described the endorsement of politicians who “undermine democracy” as “morally bankrupt and short-sighted”. The former head of the strongly pro-Israel Anti-Defamation League, Abe Foxman, described the endorsement of election deniers as a “sad mistake” .

Aipac has defended its backing of extremists on the grounds that support for Israel is more important that other issues.

“This is no moment for the pro-Israel movement to become selective about its friends,” the group said in a message to supporters earlier this year.

“The one thing that guarantees Israel’s ability to defend itself is the enduring support of the United States. When we launched our political action committee last year, we decided that we would base decisions about political contributions on only one thing: whether a political candidate supports the US-Israel relationship. Not on any other issue – just this one.”

Although some Democrats have faced calls to reject Aipac’s endorsement, a senior staffer for one member of Congress said they were not prepared to get into a public confrontation with the lobby group.

“Aipac is now an embarrassment but frankly it’s too powerful to go up against,” the staffer said. “We don’t need them pouring money in against us so we hold off on the public criticisms. But that doesn’t mean to say there are not some serious policy differences, particularly on Iran.”

Aipac is not alone.

The Democratic Majority for Israel (DMFI) was founded three years ago to bolster support for Israel within the party after polls showed younger supporters increasingly wanted to see Washington take a stronger stand in favour of the Palestinians.

Differences within the party were thrown into sharp relief recently when a row blew up over comments by the Palestinian American congresswoman Rashida Tlaib, who said there was a contradiction between backing policies that oppress Palestinians and claiming to be progressive.

“I want you all to know that among progressives, it becomes clear that you cannot claim to hold progressive values yet back Israel’s apartheid government,” she told an Americans for Justice in Palestine conference.

Although Tlaib’s comments were directed at Israeli government actions, she was denounced by fellow Democrats who accused her of questioning Israel’s right to exist. They included Debbie Wasserman Schultz, a former chair of the Democratic National Committee backed by Aipac and the DMFI.

“The outrageous progressive litmus test on Israel by Rashida Tlaib is nothing short of antisemitic. Proud progressives do support Israel’s right to exist as a Jewish and democratic state. Suggesting otherwise is shameful and dangerous. Divisive rhetoric does not lead to peace,” she tweeted.

Americans for Peace Now, a sister organisation to Israel’s Peace Now movement, backed Tlaib.

“No part of what [Tlaib] said is antisemitic. Weaponizing accusations of antisemitism cheapens the real fight against antisemitism and does nothing to make Jews safer,” it said.

Aipac responded to questions about its support of extremist candidates by saying their views on issues other than Israel were not relevant.

“Our sole factor for supporting Democratic and Republican candidates is their support for strengthening the US-Israel relationship,” said a spokesman, Marshall Wittmann.

“Indeed, our political action committee has supported scores of pro-Israel progressive candidates including over half of the Congressional Black Caucus and Hispanic Caucus and almost half of the Progressive Caucus. Our political involvement has shown that it is entirely consistent with progressive politics to support America’s alliance with our democratic ally, Israel.”