San Francisco (CNN) The welcoming cheers 2020 presidential hopeful John Hickenlooper received when he first graced the stage at California's Democratic Convention quickly crumbled into boos and jeers after he rejected socialism as the answer to Democrats' problems.

"If we want to beat Donald Trump and achieve big progressive goals, socialism is not the answer," Hickenlooper said to a crowd of more than 4,500 delegates and observers on Saturday.

Before he could get finish his next sentence, a chorus of boos along with a sea of waving "Bernie" signs overtook his speech, lasting for more than 30 seconds. The moment prompted Hickenlooper to attempt a smile and eventually break from his remarks to add, "You know, if we're not careful, we're going to end up helping to re-elect the worst president in history."

The former Colorado governor is one of 15 Democratic candidates to address the San Francisco crowd, which is known to be home to some of the party's furthest left progressives.

The moment seemed to pass until Hickenlooper started to speak about "pragmatism."

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