Phoenix (CNN) Thousands of liberal Democrats are descending on this desert city this weekend. But not Hillary Clinton.

Clinton's absence from the Netroots Nation conference, an annual gathering of nearly 3,000 progressive activists, is another sign of the uphill battle she faces in connecting with the most liberal wing of her party. And the rise of Bernie Sanders, her liberal challenger, is on full display.

"I think she's written us off," Dan O'Neil, a Sanders supporter who leads Progressive Democrats of America, told CNN. "She's written the left--the far left--off."

Indeed, Sanders is king here and passionate Clinton defenders are hard to find.

Many activists who spoke to CNN expressed skepticism about whether Clinton is really one of them, despite her lurch to the left on issues like same-sex marriage and immigration. Their reluctance to express full-throated support early in the primary was reinforced this week when Clinton declined invitations to address the gathering.

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