Take, for example, a block quotation that advocates making Election Day a national holiday. It is posted atop a stock photo of ballot boxes. And it contains no searchable text. Still, it received nearly 100,000 likes and 22,000 shares. By comparison, Hillary Rodham Clinton’s video announcing her presidential candidacy received over 79,000 likes and 41,000 shares.

“He can post a quote graphic or a long text-only Facebook status, and it doesn’t really matter what the algorithm favors,” said Laura Olin, who was in charge of the much-praised social media strategy for President Obama’s 2012 campaign.

“If it sounds like him,” she said, “his people will find it and spread it.”

And the reason Bernie Sanders’s posts sounds like him is that, for the most part, they are from Bernie Sanders. He often comes to his Senate office with quotations at the ready.

“Usually, it’s in the shower where something pops into my head,” Mr. Sanders said, adding, “I play a very, very active role in writing, literally writing, what goes up there on Facebook.”

And unlike many candidates, he does not share warm details of his daily life. “People don’t need to know what I buy in the grocery store or what the name of my dog is — I don’t own a dog, by the way — but they do need to know why billionaires are getting richer and the poor are getting poorer.”