Hillary Clinton declined to participate in a virtual presidential candidates’ forum hosted by MoveOn.org, snubbing one of the largest progressive groups that claims 8 million members.

All three Democratic candidates were invited to participate in the forum, which involved the candidates answering questions submitted by MoveOn members via video, but only Sen. Bernie Sanders and former Maryland Gov. Martin O’Malley agreed. Video of their answers was released Tuesday afternoon.

“It’s a shame that Secretary Clinton declined to participate in the MoveOn member forum,” said Anna Galland, the executive director of MoveOn.org Civic Action, in a statement to MSNBC. “She missed an opportunity to speak directly to and energize the progressive base she’ll need in her corner not just to win the nomination but also the general election, if she is the party’s nominee.”

A Clinton spokesperson declined to comment.

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MoveOn and Clinton have a long and not always an amicable history. The group started in 1998 to fight the impeachment of her husband, former President Bill Clinton. In 2007, all eight candidates for the Democratic nomination, including Hillary Clinton, participated in the group’s presidential forum. MoveOn ended up endorsing Barack Obama.

Several months later, Clinton was recorded at a closed-door fundraiser complaining that “MoveOn.org endorsed [Obama] – which is like a gusher of money that never seems to slow down.” She went on to say, “they know I don’t agree with them,” and she warned the group would “flood” caucuses with activists, including some who “intimidate people who actually show up to support me.”

Earlier this year, MoveOn worked to draft Sen. Elizabeth Warren into the 2016 Democratic presidential race, arguing she would be a better pick for the party than Clinton.

But if Clinton was worried about MoveOn’s gusher of money and ability to mobilize activists then, she clearly is not now. While MoveOn is still by far the largest group of its kind, its influence and spending power may have waned as other groups have moved into its space.

Still, Democratic strategist Mike Lux, who has spent years in the progressive movement, said Clinton made an error in skipping the forum. “I just think it’s a really bad mistake,” he told MSNBC. “Her biggest problem, I think, both in the primary and in the general is energizing the Democratic base.”

“Before this election is over, she’s going to need not only their vote – and she’ll get most of their votes, though some may stay home – she’s going to need their passion. She’s going to need them knocking on doors, donating money, talking to their friends,” Lux said. “She’s blowing that part of the base off, and with 8 million members, that’s a lot of people.”

Clinton faced some criticism this summer when she declined to speak at the Netroots Nation forum, the annual gathering of web-savvy lefties. But in the end, Clinton’s decision proved fortuitous as Sanders and O’Malley, who did attend, had their first awkward run ins with the Black Lives Matter movement.