WASHINGTON » The quotes he posts are rarely pithy, and often sayings he thinks up in the shower. The photographs he puts up sometimes show him frowning, while others show him gazing oddly into the horizon. And he does not seem to care about the importance of videos.

But somehow, Bernie Sanders, the 73-year-old senator from Vermont, has emerged as a king of social media early in the 2016 presidential campaign, amid a field of tech-savvy contenders.

His Facebook posts attract tens of thousands of likes and shares, and threads about him often break through to the home page of Reddit, where the cluster of topics rarely focuses on presidential election politics.

"I’m a grumpy old guy," Sanders joked when explaining his approach to posting online. "I know that people talk about their cats and ‘I’m walking to the grocery store and getting a can of chicken soup’ and ‘this is so exciting.’ By and large, we have not done that."

Sanders’ prominence online is all the more improbable given that he does not do many things the way social media experts say they should be done.

He has not shied away from posts of 300 words or more, with a "continue reading here" link to his personal website.

Sanders, an independent who describes himself as a socialist, has stuck to an idiosyncratic method: posting images that share a quote, which he has either written himself or dug up from a historical figure and then superimposed onto a photograph. (President Theodore Roosevelt and President Dwight D. Eisenhower are among those he has recently cited.)

Social networking sites like Facebook recommend that when users post text, they do so with searchable words that would be attractive to newsfeed algorithms and search engines.

But Sanders’ team rarely uses buzzy introductory text when sharing his posts, leaving the chances of their going viral to users who stumble upon them. Fortunately for Sanders, who is seeking the Democratic nomination, he has loyal followers who somehow always know how to find his latest musing.

Take, for example, a block quote that advocates making Election Day a national holiday. The quote 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 more than 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 Barack Obama’s 2012 campaign. "If it sounds like him," she said, "his people will find it and spread it."

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

"Usually, it’s in the shower where something pops into my head," 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."

A former journalist who began sending newsletters to his constituents in the early 1990s, Sanders relishes writing. He carries yellow legal pads with him wherever he goes, "for a little jabbering," and their contents are often turned verbatim into a posting.

A typical quote from him on his Facebook page, which often deals with income inequality, says, "We must rebuild American manufacturing and rewrite our trade agreements so that our largest export is not our jobs."

"I think the people that have the most success on Facebook, they’re developing an authentic method and sticking to it," said Anton Vuljaj, director of advertising at IMGE, a consulting firm. "He’s matching what he’s saying online to what he’s doing offline."

While Sanders’ popularity cuts across social media platforms, it appears most pronounced on Facebook. He did not start his campaign with a big announcement event, and he did not enjoy the explosion of interest that Sen. Ted Cruz of Texas and Sen. Rand Paul of Kentucky experienced when they declared that they were seeking the Republican nomination.

Sanders had 1.3 million Facebook interactions, compared with 5.6 million for Cruz and 2 million for Paul, according to data provided by Facebook.

But since their announcements, the popularity of Cruz and Paul on Facebook has tempered, while Sanders’ has risen. In a seven-day stretch leading up to May 3, Sanders had 5.3 million interactions, compared with 1.2 million for Paul and 1.7 million for Cruz.

On Reddit, he is similarly popular. The site’s home page, which is powered by the upvotes of users on a topic thread, is often filled with viral news and esoteric, humorous discussions; politics is often found only on a subreddit. But Sanders is one elected official who has on occasion leapt over the barrier.

Among politicians, he is one of the most frequent posters to the site, and nearly a quarter of the top most-voted politics posts of all time on Reddit are about or by Sanders.

But Sanders has not eclipsed everyone else in the 2016 field on the social media front. Clinton’s videos are viewed by hundreds of thousands, Paul and Cruz have large and dedicated armies of supporters, and Jeb Bush has built a following by making most of his major announcements online.

But for a candidate who performs poorly in the polls, Sanders appears to be everywhere. And like many of his positions over the years, his social media tactics are unlikely to change with the times.

"I’m not some kind of tech nerd, I really am not," Sanders said. "But I have always believed in communication, and not just photo ops and stuff, but educating people, and communicating with people about the real work that we’re doing."