Two of the Democratic Party’s core institutions are challenging a bipartisan consensus on Israel and Palestine that has dominated American foreign policy for more than a decade.

The Center for American Progress, the party’s key hub of ideas and strategy, and Media Matters, a central messaging organization, have emerged as vocal critics of their party’s staunchly pro-Israel congressional leadership and have been at odds, at times, with Barack Obama’s White House, which has acted as a reluctant ally to Benjamin Netanyahu’s Israeli government.

The differences are ones of tone – but also of bright lines of principle – and while they have haven’t yet made any visible impact on Democratic policy, they’ve shaken up the Washington foreign policy conversation and broadened the space for discussing a heretical and often critical stance on Israel heretofore confined to the political margins.

The daily battle is waged in Media Matters’ emails, on CAP’s blogs, Middle East Progress and ThinkProgress and most of all on Twitter, where a Media Mattters official, MJ Rosenberg, regularly heaps vitriol on those who disagree as “Iraq war neocon liar” (the Atlantic’s Jeffrey Goldberg) or having “dual loyalties” to the U.S. and Israel (the Washington Post’s Jennifer Rubin). And while the Center for American Progress tends to walk a more careful line, warm words for Israel can be hard to find on its blogs.

Events of recent years such as GOP attacks on Obama as insufficiently loyal to Israel, Israel’s controversial raid on a Turkish ship bound for Gaza and debates over the Iranian nuclear program have deepened the divide between some on the Democratic left and the party’s mainstream foreign policy apparatus.

“Like segregation in the American South, the siege of Gaza (and the entire Israeli occupation, for that matter) is a moral abomination that should be intolerable to anyone claiming progressive values,” wrote Matt Duss, a CAP policy analyst and the director of Middle East Progress, last year, after an Israeli raid on a flotilla challenging the blockade of Gaza turned violent.

The two groups’ push is part of a larger revival of the liberal American Israel lobby, though one that has yet to make a policy impact. Stalwarts of the anti-settlement movement like Peace Now have new, more politically engaged counterparts like J Street and see their views reflected increasingly in the party’s central institutions. They represent – they hope – the Democratic Party’s future, if not its present, and have taken heart from recent criticism of Israel by Defense Secretary Leon Panetta and Secretary of State Hillary Clinton.

The shift is vividly reflected in the current debate over how the U.S. should handle the fledgling Iranian nuclear program. With both Obama and congressional Democrats working to increase pressure on what they view as alarming Iranian nuclear efforts, the Center for American Progress and Media Matters have made the case that both Iran’s belligerence and its level nuclear sophistication have been overstated – in some cases attacking hawkish hyperbole or Republican rhetoric, in others going after claims by the administration.

In one recent item, for instance, ThinkProgress National Security reporter Eli Clifton took issue with a Quinnipiac University poll that made reference to Iran’s “nuclear program.” The belief that such a program exists undergirds the Obama administration’s drive for sanctions, and was recently bolstered by a report from the International Atomic Energy Agency, which wrote of “increasing” concerns, though not definitive evidence.

“Such assertions, and the resulting polling statistics, serve to tilt public opinion toward preemptive military action when intelligence reports paint a far more complex picture of Iran’s nuclear program and the extremely risky outcomes of an Israeli and/or U.S. airstrike,” Clifton wrote.

Another recent column on the CAP website, one of several to prompt behind-the-scenes outrage from the powerful pro-Israel group AIPAC, featured Eric Alterman accusing AIPAC of campaigning for war in Iran, which Alterman described as its “big prize.”

Over at Media Matters, Rosenberg, a former AIPAC staffer turned apostate, labels American Israel hawks “Israel-firsters” and recently blasted Rep. Brad Sherman, a California Democrat, for pushing a sanctions on Iranian civilian aviation that would be “the most ugly expression yet of this country’s almost bizarre obsession with punishing Iran, its people along with its government.” (Sherman spokesman Ben Fishel, a former Media Matters staffer, said the organization “would agree with” Sherman if it understood how civilian planes were being used to ferry arms to the Syrian government.)

ThinkProgress also scrambled to call into question an alleged Iranian plot to assassinate Saudi diplomats in the United States, though the charges were leveled by Attorney General Eric Holder, a longtime Democratic Party stalwart. “With analysts and the media still scratching their heads over what to make of a convoluted plot alleged to have been hatched by an Iranian American in collusion with Mexican drug cartels,” Clifton wrote, “[conservative think tanks] – along with their friends in Congress — are quickly declaring the end of diplomatic strategies to curb Iran’s nuclear program and regional ambitions.”

The villain: AIPAC. “It would appear that AIPAC is now using the same escalating measures against Iran that were used before the invasion of Iraq,” Clifton wrote in August.

Clifton’s post and others like it, two sources said, drew a furious reaction from the pro-Israel group, whose executives called CAP chairman John Podesta and other senior officials at the organization to complain.

“There’s two explanations here – either the inmates are running the asylum or the Center for American Progress has made a decision to be anti-Israel,” said Josh Block, a former spokesman for AIPAC who is now a fellow at the center-left Progressive Policy Institute. “Either they can allow people to say borderline anti-Semitic stuff” – a reference to what he described as conspiracy theorizing in the Alterman column – “and to say things that are antithetical to the fundamental values of the Democratic party, or they can fire them and stop it.” (Alterman called the charge "ludicrous" and "character assassination," noted that he writes for Jewish publications, and described himself as a "proud, pro-Zionist Jew.")

An AIPAC spokesman, Ari Goldberg, declined to comment on CAP’s views. But the suggestion that AIPAC is leading an Iraq-style drive for war with Iran also angered leading Jewish Democrats, many of whom are close to AIPAC.

“There’s a great difference between the widespread concern for Iran within the Democratic and Jewish communities versus the far right. Some extreme right-wingers may be beating the drums for war, but the vast mainstream — certainly including AIPAC — is most definitely not,” said David Harris, the CEO of the National Jewish Democratic Council, when asked about the AIPAC’s statements. He noted that even liberal, pro-Israel groups like Peace Now and J Street shy away from putting AIPAC at the heart of a pro-war cabal.

CAP officials have told angry allies that the bloggers don’t speak for the organization, and senior fellow Brian Katulis – whose work is more standard Clinton-Democrat fare – stressed that in an email.

“I think there are different voices on the Think Progress blog and some individual analysts - and some of that work, especially the blog, is I think aimed at reporting on and reflecting one aspect of the diversity of the views among the broad progressive community,” he said. “But what one blogger or analyst may write isn’t necessarily indicative of what our policy recommendations are for the administration or Congress when I’m doing meetings with our friends in government.”

The director of CAP’s national security program, Ken Gude, also drew a distinction between the blog, which is CAP’s loudest megaphone, and its less confrontational policy work.

“There’s a distinction here that we have between the policy work that we do and the blogging work that we do,” he said. Middle East Progress “is clearly a progressive blog and it does respond to arguments that are made most forcefully by conservatives and it responds in that way.”

Gude also said the Center’s experts view the allegations of an Iranian assassination plot as credible, despite initial doubts, and said he wasn’t sure whether that perspective had been reflected on its blogs, or why not.

In interviews, several ThinkProgress officials described the Center’s goals differently. Two of them suggested that criticizing the Israeli government and raising doubts about allegations against Iran serve a useful political purpose: They open political space on Obama’s left, and give the president room to maneuver.

Gude denied that motive.

“There is no decision on the part of the Center for American Progress to push any line that would be to the left of [the Administration],” he said.

AIPAC and its allies have not been satisfied by those explanations. “To suggest that the organization is not responsible for people who are ‘just bloggers’ is ludicrous and insulting to people’s intelligence,” Block said. But CAP has refused to give ground, and while CAP’s top officials didn’t respond directly to POLITICO, Gude said he was unaware of Jewish Democrats’ concerns.

The seams sometimes show in the organization, however. Podesta, who recently stepped down from his longtime position as CAP’s president, “always wanted to stay out of Israel stuff from the beginning, because it’s a no-win issue for them,” a liberal Israel policy thinker and CAP ally said. “They’re obviously a progressive place, but if you want to attract a mainstream Clinton, New Democrat milieu, you can’t really do real progressive Israel stuff.”

But the fact remains that the Center’s most audible voices on the Middle East aren’t the former Clinton staffers who populate much of the organization, and they come from different foreign policy traditions. Duss, a confrontational presence on Twitter but typically a more careful blogger, places himself in what’s sometimes called the “realist” stream of American foreign policy – he was an intern for Anthony Cordesman of the Center for Strategic and International Studies, for instance. It’s the stream from which many Washington figures who would prefer the U.S. push Israel harder drink.

“This is where James Baker and George H.W. Bush were, this is where Brent Scowcroft is, this is where Tom Pickering and Colin Powell are – this is not crazy stuff, we’re talking about mainstream, bipartisan positions,” said Jeremy Ben Ami, the executive director of J Street, which has sought in recent years to build an American “pro-Israel, pro-peace” lobby.

Duss’s deputies hail from farther to the left: Clifton and his colleague Ali Gharib came to CAP from Inter Press Service; their work is still published, by agreement with the Center for American Progress, on the blog of the Inter Press Service’s Jim Lobe, a stalwart of a range of foreign policy views well to the left of the Democratic Party. He was a fierce foe, for instance, of Bill Clinton’s Bosnian interventions, complaining bitterly in 2006 that “Abraham Lincoln was canonized for invading the South to prevent its secession, but [Serb leader and convicted war criminal Slobodan] Milosevic was damned for trying to protect Yugoslavia’s territorial integrity.”

Duss dismissed his staffs’ intellectual roots – “they’re just two very good reporters” – or the implication that they were saying anything radical.

“That recognition – there are two narratives here, there are actually two sides to this – it’s a sad statement on the debate in DC that just saying that gets you qualified as anti-Israel,” he said.

But that more liberal stream of foreign policy thinking, in exile in the Clinton years, was vindicated for some Democrats when its leading voices opposed President Bush’s war in Iraq – a position the rest of the party came to late if at all. And CAP’s new views are, Duss said, in part generational.

“I’m really interested in the way in which America’s experience in the Middle East in the last decade has informed this younger generation of analysts and journalists and veterans,” he said.

Duss says he’s mischaracterized by his critics as anti-Israel. He is quick to note that he sympathizes with Israel, in part from his personal roots in American evangelical Christianity and that if American criticism of Israel should be harsher, it should also be done with the recognition that Israel is a democracy that should be held to high standards. Iran, meanwhile, is “abusing their own people, they support terrorism, and they say all sorts of horrible things about the U.S. and Israel,” he said.

But if CAP is at times cautious or muddled about its goals, Media Matters, by contrast, backs Rosenberg’s line, and makes no apologies for his sharp criticism of Democrats.

“Conservative misinformation on specific issues knows no partisan bounds,” said Media Matters executive vice president Ari Rabin-Havt. “There’s a difference between ideology and political party.”

And Rosenberg told POLITICO that his cadre of writers is looking less to sway votes on Capitol Hill today than to shift the Democratic Party’s conversation and its younger generation.

“We’re playing the long game here,” said Rosenberg.

The participants in the endless, bitter Israel policy arguments all demand a variety of labels: pro-Israel, pro-Palestinian, pro-American. Everyone argues that his case is win-win. But the new tone in Washington is also one that straightforwardly pro-Palestinian voices see as a welcome change, if one that has yet to be accompanied by a shift in American policy.

“What is actually happening is that the discourse that lot of people in the Palestine solidarity community and activists have been engaging in is starting to break down the walls of the Washington bubble,” said Ali Abunimah, a longtime activist and the co-founder of the site Electronic Intifada. “But political intimidation from Israel’s supporters is still a much more powerful force than any change in thinking at the CAP.”