Filmmaker Michael Moore apparently touched a nerve Saturday when he suggested that former Vice President Joe Biden still had to earn young voters' support before the presidential election.

"Joe Biden cannot defeat Trump w/o young people. He lost their vote in nearly every primary!" Moore tweeted.

"Not just the under-30 vote but the under-40 vote, too. And, in a few places, the under-50s! Ignore this at your own peril. A letter 2 Joe from the youth of America," he added, sharing an open letter to Biden published by The Guardian.

His comments came after Sen. Bernie Sanders, I-Vt., suspended his presidential campaign, essentially leaving Biden, a perceived moderate, as the presumptive Democratic nominee.

Signed by several left-leaning groups, the letter tells Biden he can't rely on an anti-Trump and "return to normalcy" message during his presidential campaign.

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"Why would we want a return to normalcy? We need a vision for the future, not a return to the past," the letter read. It listed a series of policies that it said were key for Biden to earn the support of the younger generation.

Those included "Medicare for all," which Biden has repeatedly opposed, alongside other liberal proposals such as free tuition. It also called for specific appointments, like economist Joseph Stiglitz for Biden's national economic council.

"Commit to appointing progressive elected officials who endorsed Bernie Sanders or Elizabeth Warren as transition co-chairs, such as representatives Ro Khanna, Pramila Jayapal, Ayanna Pressley or Katie Porter," the letter said, referring to a series of House members.

After Moore's tweet, he started trending on Twitter. Many either dismissed his focus on younger voters or urged him to support Biden.

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The incident highlighted an ongoing divide between moderates and more liberal members of the Democratic Party.

Moore previously caught headlines for his comments on the 2020 race. He indicated that a moderate candidate would lose to Trump while a more liberal candidate would do the needed work of energizing the Democratic base.

Moore used that warning to make his case for a candidate such as Sanders -- whom he endorsed -- urging Democrats not to nominate another "Republican-lite" candidate like former Democratic nominee Hillary Clinton.

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While suggesting his party still has a fighting chance, Moore said that if the 2020 elections were held today, Trump would lose the popular vote by a bigger margin than he did in 2016 but still win the electoral vote.

"I think if the election were held today -- Hillary won by 3 million popular votes. I believe whoever the Democrat is next year is going to win by 4 to 5 million popular votes," Moore told Democracy Now in an interview posted Thursday.