WATCH: Human Rights Campaign's Chad Griffin Rallies With Hillary Clinton in Iowa

Human Rights Campaign president Chad Griffin joined Democratic presidential hopeful Hillary Clinton on stage in Iowa Sunday, reaffirming his group's endorsement -- which has become a point of contention on the campaign trail.

"She doesn't just voice her support, or vote her support for our community, she has been our partner in this fight and always willing to go to battle when we need her," Griffin said on stage. "She has the experience and the determination and the skills that will allow her to make meaningful change from the moment she walks into the Oval Office."

Last week, 32 board members of the HRC voted unanimously to endorse Clinton for president. Fellow Democratic presidential candidate Bernie Sanders, who has a more consistent record when it comes to LGBT issues, slammed the HRC's endorsement implying that as the largest and most powerful LGBT organization in the country, it is part of the "political establishment."

He later clarified those remarks in an interview on MSNBC, focusing his cricitism on the leaders of HRC and other groups that endorsed Clinton. He said it's the leadership, not the groups, that are part of the political establishment.

The HRC's original endorsement video made no mention of Sanders and instead initially attacked Republican candidates over marriage equality. And Griffin reiterated that, "The leading Republican candidates for president, they're still living in the dark ages." Griffin noted some who support reinstating the "don't ask, don't tell" policy and want to overturn marriage equality. He never mentioned the argument over whether Clinton and he are part of the "political establishment."

But the news after the endorsement quickly became about Sanders' comments and less about Republicans, with HRC tweeting about its "disappointment in Sanders' attacks." Meanwhile, HRC has also faced criticism from LGBT voters. Noted out journalist Michelangelo Signorile wrote "How an Early Endorsement From Largest LGBT Group May Reveal Hillary Clinton's Worst Fears" for Huffington Post Gay Voices, suggesting the Clinton campaign is "calling in its chips" because it's struggling.

A Washington Bladeheadline on Sunday declared "'Establishment' Criticism of HRC Strikes a Chord." Reporter Chris Johnson spoke with activists who said Sanders got it right even when it sounded as if he'd labeled the entire group as establishment.

Griffin took over HRC as president in 2012 and is a former aide to Bill Clinton, campaigning for him in 1992 and then serving on the former president's communications team during the first term. Griffin is also from Hope, Arkansas and when introducing Hillary Clinton to an HRC crowd last year, Griffin shared slides of himself as a teenager in Arkansas alongside the state's first lady, joking that "I've known Hillary Clinton for a long time, like a really long time -- like a really, really long time."

Clinton reminded the audience on Sunday about their long history.

"I've known Chad Griffin since he was a young boy in Arkansas -- who has made good," she told the audience. "Last time I saw him, he pulled out a photo of the two of us so many years ago. You know, the way you date my photos is by hair styles. It's kind of an archeological exercise. But I know a little bit about what it was like for him growing up in Arkansas, learning about who he was and is, looking for understanding, looking for an opportunity to be fully himself, and I so respect that journey that many of you in this crowd tonight have taken. And I want that journey to be easier and smoother for young people today who have to do it for themselves."

HRC highlights Clinton's past record of support for LGBT issues, including helping to lead on bills to protect LGBT workers from employment discrimination and working on LGBT equality with the United Nations.

But Sanders has also been a reliable supporter of LGBT equality, supporting the Employment Non-Discrimination Act when it passed the Senate in 2013 and even calling on President Obama to hasten his evolution and support marriage equality in 2011. Sanders is a co-sponsor of the federal LGBT-inclusive Student Non-Discrimination Act and has consistently voted against bills seeking to amend the Constitution to ban same-sex marriage, while co-sponsoring a bill that would repeal the remaining portions of the so-called Defense of Marriage Act. He has a perfect score of 100 percent on the Human Rights Campaign's latest congressional scorecard.

Watch Griffin endorse Hillary Clinton: