Democratic hopeful Bernie Sanders went nuclear this week when he suggested that former Secretary of State Hillary Clinton may not be “qualified” to be president.

Sanders, who has since walked back the remark, said he was merely responding to efforts voiced by the Clinton campaign via CNN to “disqualify” his candidacy by going negative in order to “bury” Sanders in New York.

In fact, Sanders’ blistering attack echoes an earlier challenge voiced by one of Sanders' key surrogates: Hawaiian Congresswoman Tulsi Gabbard.

When she defected from the Democratic National Committee to endorse Sanders last month, Gabbard said she did so because she felt Clinton lacked the “judgement” and “foresight” to be commander in chief. In an oped for Time magazine explaining her rationale, Gabbard singled out Clinton’s 2002 vote to authorize the Iraq war and her pro-interventionist stances on Libya and Syria as reasons why she felt Clinton was the wrong choice to be the Democratic nominee

Clinton has acknowledged many times that her 2002 Senate vote authorizing military intervention in Iraq was a mistake. But Gabbard, an Iraq war veteran and member of Hawaii’s Army National Guard, took it a step further. In an interview with MSNBC’s Rachel Maddow, Gabbard suggested that Clinton should “ actually apologize ”: “I have not heard Secretary Clinton actually apologize to my brothers and sisters in uniform, military families for her vote for the Iraq war,” Gabbard told Maddow.

It was a signal challenge to Hillary Clinton. Whether Sanders chooses to take up this line of attack during New York’s already overheated primary or continue to use Gabbard as a surrogate thorn in Clinton’s side will be interesting to watch play out.

Gabbard, who now often warms up the crowds at Sanders rallies, is certainly well-positioned to take on Clinton’s battlefield chops. She speaks emotionally of the “high human cost” of the Iraq war, which she experienced firsthand during her first deployment to Iraq in 2005, when she was in an Army National Guard medical unit. (One of her duties was cataloguing the names of American soldiers killed and wounded.) It’s an issue she feels has been woefully absent from the media circus and debate surrounding both the Republican and Democratic primaries thus far.

Speaking on MSBC , Gabbard slammed Clinton for being an “architect” of the U.S. bombing intervention in Libya that led to the overthrow of Muammar Gaddafi, and for advocating a no-fly zone in Syria which Gabbard says could further imperil American service members and risk military conflict with Russia as well.

“If she says she’s learned from Iraq, then why is she championing this war to overthrow the Syrian government of Assad, and essentially promising to escalate the war if she’s elected as president by implementing a so-called no-fly zone?” Gabbard demanded on MSNBC

In an interview with CNN ’s Jake Tapper last month, Gabbard portrayed Clinton’s support for American intervention as a lesson of unintended consequences: “In each instance—Iraq, Libya and Syria— the Islamic terrorist groups have become stronger as a result of the regime change interventionist action rather than the opposite, which actually should be our objective.

“Does that serve our best interest? Does it serve the safety and security of the American people? Taking our country and our men and women into war without thought and foresight for what the consequences truly are?”

These are profound questions, should Sanders choose to pose them directly to Clinton at the next scheduled debate on April 14. Of course, Sanders may be more comfortable delegating this level of criticism, for fear of dovetailing into the kind of venomous attacks Clinton has faced ad nauseam from the right over Benghazi and the whole Libya debacle.

Ironically, Gabbard’s call for Clinton to “apologize” is mirrored by a call from family members of victims of the Sandy Hook mass-shooting, who want Bernie Sanders to “ apologize ” for opposing their effort to sue the manufacturer of the assault rifle that massacred their children.

"He owes families like mine and families involved in the lawsuit an apology because he really has had a callous dismissal of our concerns and our fight for justice,” Erica Smegielski, the daughter of the Sandy Hook Elementary School principal who was killed at Newtown, told CNN on Wednesday. “He is picking the gun lobby over our families,” Smegielski said of the Vermont senator.

For her part, Gabbard appears to have no qualms about crossing into right-wing territory. Last fall, she slammed President Obama for refusing to use the phrase “radical Islam” in relation to ISIL and al Qaeda (for fear of equating Islam with terrorism and playing into the battle of civilizations).

Gabbard also openly mocked Clinton’s successor, Secretary of State John Kerry, for emphasizing the economic roots of terrorism, saying that Kerry thinks, "if we give them [Islamic extremists] $10,000 and give them a nice place to live that somehow they're not going to be engaged in this fighting.”

That line earned her fawning coverage from Fox News and other conservative outlets. Far from being a “darling of the right” however, Gabbard claim she is speaking out as a non-interventionist, taking a pragmatic stance that cuts across party lines.

In her view, it is impossible to understand the spread of ISIL—or the threats posed by al Qaeda and its Syrian counterpart, the Al-Nusra Front—without discussing these group’s extremist theology. “Unless you accurately identify who your enemy is, you cannot effectively fight them,” she argues. “We must identify the enemy in order to figure out what is the approprirate strategy to defeat them.”

Gabbard views the Iraq war, Gaddafi’s overthrow and further military intervention in Syria as part of a continuum of failed and misguided nation-building efforts by the West.

Gabbard's own background lends itself to this maverick critique. When she was first elected in 2013, she was the first Hindu American in Congress. (Though she is American Samoan, she converted to Hinduism as a teenager.) She was also, at age 31, the youngest woman in Congress.

Some progressives have accused Gabbard of promoting Islamophobia. They point to her ties to the Hindu nationalist Indian Bharatiya Janata Party (BJP) and its controversial prime minister, Narendra Modi, who has been widely criticized for condoning hatred and violence against India's Muslim minority. Many of Gabbard’s stateside donors and supporters are big supporters of BJP.

But Gabbard’s endorsement of Sanders is also in keeping with her own trajectory as an underdog who earned her congressional seat thanks to a primary upset victory against former Honolulu Mayor Mufi Hannemann . (The Honolulu Star-Advertiser described her win as the "improbable rise from a distant underdog to victory.”)

Gabbard may feel that her political future lies more with Sanders’ progressive base than with the party establishment. When she resigned from her plum post of vice chair of the the DNC last month, she said she did do because she could not in “good conscience” remain neutral in the race—which is a requirement for serving on the DNC. But for months, Gabbard had been openly feuding with DNC chair Debbie Wasserman Schultz over Wasserman Schultz’s effort to restrict the number of Democratic debates under the guise of party unity.

Gabbard’s fight with Wasserman Shultz and the DNC was in some sense a proxy fight for the wider contest between Sanders’ populist insurgency and Clinton as heir to the Democratic Party establishment. By aligning with Sanders, Gabbard appears to be looking to carve out a new strain of progressivism within the Democratic Party—and a prominent role for herself in it. By sticking her neck out for Sanders, Gabbard puts herself in the position to gain greater media visibility; as a Clinton supporter she'd be just one face in a very large political crowd.

Gabbard’s positioning may also reflect her decision to align with the wishes of her largely progressive base in Honolulu and Oahu. Clearly her endorsement has been a boon to Sanders, who swept the Hawaiian caucus on March 26 with 70.6 percent of the vote to Clinton’s 29.2 percent.

Also endorsing Sanders in advance of that contest was Kaniela Ing, Hawaii’s youngest state legislator , who said he was backing the Vermont governor as “the only candidate willing to walk the talk to get big money out of politics.” (Ing’s decision to endorse Sanders—in contrast the majority of Hawaii’s elected Democrats went with Clinton—paid off: Ing won his primary challenge and is currently campaigning in the general election as Maui's only elected “Berniecrat.”)

Like Ing, Gabbard is playing the long game, sacrificing her ties to the Democratic Party establishment on a bet that Sanders’ left-right insurgency is the ticket to ride in this election.