Every four years, presidential candidates from the two major parties do the same thing: Democrats move to the left, Republicans to the right, in an effort to win the nomination. Then, after they’ve locked that down, both move back to the center to try to win the White House.

Overall, Americans are moderate. Across the electorate, about 20 percent of voters are each of the two extremes, far left and far right. Another 25 percent on each side lean left or lean right. So 90 percent of voters have already made up their minds.

That leaves 10 percent of the populace, and they’re right in the middle. They decide elections. Democrats voted for President Reagan. Republicans voted for President Obama. And that 10 percent in the middle maybe didn’t vote for President Trump, but they did vote against Hillary Clinton.

Former Vice President Joe Biden is throwing all that history to the wind. The presumptive Democratic nominee’s first move after securing the nomination was to slide even further left on the ideological scale.

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Shortly after Sen. Bernie Sanders suspended his campaign last week, Biden reached out to the Vermont socialist’s supporters, expressing support for expanding Medicare eligibility to Americans 60 and older and calling for new efforts to forgive student loans — two pillars of the Sanders platform.

The move was clearly calculated. Biden knows he can’t win without support from a faction that has become known as the “Bernie Bros,” some of whom stayed home in 2016 after Clinton defeated their hero for the nomination.

Worse, other Bernie Bros actually switched over to Trump. One study showed that about 12 percent of Sanders backers voted for Trump in the general election. That’s likely how Trump pulled off surprise wins in states that normally vote Democratic, like Wisconsin and Michigan, as well as grabbing Pennsylvania, a toss-up state.

Biden is trying to walk a tightrope many more-skilled politicians have slipped off, plummeting to their political deaths. Biden needs to reach out to Sanders’ supporters so they’ll get on board, but if he goes too far left, he’ll leave himself open to attacks from Trump that he’s too liberal for America — attacks Trump was preparing to use against the Democratic Socialist.

Biden won the endorsement Monday of Sanders, who said that “today I am asking all Americans, I’m asking every Democrat and I’m asking every independent, I’m asking a lot of Republicans, to come together in this campaign to support your candidacy, which I endorse, to make certain that we defeat somebody who I believe, and I’m speaking just for myself now, is the most dangerous president in the modern history of this country.”

But the Bernie Bros won’t go quietly.

“With the utmost respect for Bernie Sanders, who is an incredible human being & a genuine inspiration, I don’t endorse Joe Biden,” Sanders 2020 national press secretary Briahna Joy Gray wrote on Twitter shortly after the endorsement. “I supported Bernie Sanders because he backed ideas like #MedicareForAll, cancelling ALL student debt, & a wealth tax. Biden supports none of those.”

Even Sanders isn’t going away. In his exit speech last week, he said, “I will stay on the ballot in all remaining states and continue to gather delegates.”

“While Vice President Biden will be the nominee, we must continue working to assemble as many delegates as possible at the Democratic National Convention, where we will be able to exert significant influence over the party platform and other functions,” Sanders said.

Sanders supporters know they have clout. Shortly after Sanders suspended his campaign, a collective of eight groups — including Alliance for Youth Action, March for Our Lives Action Fund and the Sunrise Movement — issued a warning to Biden.

“Messaging around a ‘return to normalcy’ does not and has not earned the support and trust of voters from our generation. For so many young people, going back to the way things were ‘before Trump’ isn’t a motivating enough reason to cast a ballot in November,” the groups wrote.

“While you are now the presumptive Democratic nominee, it is clear that you were unable to win the votes of the vast majority of voters under 45 years old during the primary. With young people poised to play a critical role deciding the next President, you need to have more young people enthusiastically supporting and campaigning with you to defeat Trump.”

But Nomiki Konst, a Sanders surrogate who worked on party reforms on his behalf, isn’t optimistic.

“We can try all we want to use our leverage as a movement but, at the end of the day, I wouldn’t expect anything coming from the establishment, the Biden campaign or the Democratic National Committee as a way to bring in the base,” she told The Daily Mail.

“I think they want power — and I think they want money.”

*Joseph Curl ran the Drudge Report from 2010 to 2014 and covered the White House for a dozen years. He can be reached at [email protected] and on Twitter at @JosephCurl. A version of this article ran previously in The Washington Times.