Sen. Bernard Sanders has amassed a presidential campaign team of pit bulls skilled in the art of internal party warfare — and in many cases is still grinding axes over the way he was treated by the Democratic Party in his 2016 run for the White House.

Three members of his team didn’t even back Hillary Clinton, the Democratic nominee, and instead supported the Green Party in the general election.

Others have made a career of ripping the very people Mr. Sanders now faces in the 2020 Democratic primaries.

Among those is David Sirota, his senior adviser and speechwriter who has earned a reputation for combativeness online. He has deleted 20,000 of his tweets, many of them harsh attacks on other Democrats, according to Politico.

Mr. Sirota and the other political warriors seem to belie the image the septuagenarian socialist enjoys among the voting public.

“These people are attack dogs and make it look like Bernie’s planning on a slash-and-burn campaign,” said one longtime Democratic operative with deep presidential campaign experience. “Either Bernie’s naive, which I don’t think he is, or it’s a little bit of a recognition I’m going to say one thing and do the complete opposite.”

Joining Mr. Sirota on the Sanders 2020 team are Nina Turner, the campaign co-chairwoman and a former Ohio state senator who was offered a spot on the Green Party ticket in 2016; Winnie Wong, a senior adviser who in 2017 tweeted that Mrs. Clinton is “the worst person in the world”; and Briahna Joy Gray, a press secretary who voted Green in 2016 and has repeatedly attacked other Democrats on Twitter.

The Sanders campaign also employs Chuck Rocha, a senior adviser who was part of the 2016 campaign, too. As was reported then, Mr. Rocha was convicted in 2013 of stealing money from the United Steelworkers, where he served as political director, and blowing his ill-gotten loot on golf junkets and tickets to the Detroit Red Wings’ 2009 Stanley Cup run.

It’s not surprising that Mr. Sanders would have some bare-knuckled partisans on his team, given that many of his supporters still bristle over the last presidential election, according to political professionals.

“A lot of people around Sanders believe they should have been tougher on Clinton earlier in the 2016 campaign,” said Ron Faucheux, a former Louisiana lawmaker turned political analyst in Washington. “Some of this new toughness is a result of that. This will be much harsher than was the 2016 Democratic nomination battle. Nobody’s getting an easy ride.”

The Sanders campaign didn’t respond to interview requests from The Washington Times.

Presidential primaries can be nasty affairs, as the 2016 installment showed.

President Trump and his Republican opponents engaged in the kind of insult war that would thrill a late-night comic. On the Democratic side, things got so bad that the Democratic National Committee accused Mr. Sanders of stealing Mrs. Clinton’s data, and the Sanders campaign sued the DNC for breach of contract.

Later, leaked emails showed then-DNC Chair Debbie Wasserman Schultz calling the Sanders campaign manager a liar and another top DNC staffer pondering how to push negative press coverage about Mr. Sanders.

This year, Mr. Sanders is already rankling opponents with his team — and particularly his hire of Mr. Sirota, who from his perch as a columnist for the left-wing Guardian newspaper took regular shots at non-Sanders 2020 presidential candidates.

One December piece examined the voting record of former Rep. Beto O’Rourke, saying the Texan backed the oil industry and strict immigration policies during his time in the House.

Sens. Cory A. Booker, Kamala D. Harris and Kirsten Gillibrand and former Vice President Joseph R. Biden also took heat from Mr. Sirota’s pen.

His hire by the campaign sparked a debate within Democratic circles about whether Mr. Sirota had been writing takedowns of other 2020 Democrats while he was in talks with Mr. Sanders.

The Guardian denied it.

Charlie Cook, a veteran political analyst, said he doubted that sharp elbows on Mr. Sanders‘ team will matter much to voters.

“In my 47 years in politics, I have never seen Democrats as focused on and determined to win the presidency as now,” he said. “Sure, each of the candidates will have attack dogs, but the mindset in the Democratic Party is such that they will have little effect. Electability is rarely an important factor in primary voters’ minds, but in 2020, unelectability may be if a candidate is perceived as not very strong against President Trump.”

South Carolina legislator Terry Alexander, who backed Mr. Sanders in 2016 and is doing so again in 2020, said supporters have a reason to be upset at Democrats after the 2016 election.

Mr. Alexander said he still sees Mr. Sanders as the best pick to beat Mr. Trump. Although he prefers that Mr. Sanders not attack other Democrats unnecessarily, he said all hard feelings will be forgiven in the general election.

“They’ll get over it,” he said. “I’m sensing it will be Bernie Sanders who gets the nomination, and I hope he does. But whoever gets it, I will endorse that person wholeheartedly because I think the Democratic Party will come together to get rid of Donald Trump.”