The calendar may read 2019, but for some, it's still 2016. 

Some professional Democrats are harboring bad blood related to the party's 2016 primary, a dynamic that's become clear in the early days surrounding Vermont Independent Sen. Bernie Sanders' presidential launch. 

It's unclear how much resentment rank-and-file Democratic voters still feel after the tough primary, which left some Sanders supporters feeling like the race was rigged against them and Hillary Clinton supporters frustrated that Sanders' orbit didn't fall faster in line behind her. 

But the fissures that do still exist are clear in recent stories that call into question whether Sanders can put the past behind him and capture the party's 2020 presidential nomination, a question First Read identified last week as central to Sanders' bid.

The dynamic is most clear in Politico's new story on Sanders' post-primary travel in support of Clinton, the premise of which hinges on Sanders' use of a "a carbon-spewing private jet" amid his calls to combat global warming and the fossil fuel industry. 

Zac Petkanas, Clinton's former rapid response director, panned Sanders in a particularly blunt quote: 

"I’m not shocked that while thousands of volunteers braved the heat and cold to knock on doors until their fingers bled in a desperate effort to stop Donald Trump, his Royal Majesty King Bernie Sanders would only deign to leave his plush D.C. office or his brand new second home on the lake if he was flown around on a cushy private jet like a billionaire master of the universe," he told the outlet. 

Michael Briggs, a spokesman on Sanders' 2016 presidential bid, responded by panning Clinton and her staff as "total ingrates." 

"You can see why she’s one of the most disliked politicians in America. She’s not nice. Her people are not nice...[Sanders] busted his tail to fly all over the country to talk about why it made sense to elect Hillary Clinton and the thanks that [we] get is this kind of petty stupid sniping a couple years after the fact," he said. 

It's not the only reincrimination from 2016 in recent days—New York City Mayor Bill de Blasio, the possible presidential candidate who served as Hillary Clinton's Senate campaign manager back in 2000, panned Clinton in Iowa for her "focus on Trump" over "kitchen-table issues." And he added that Clinton's camp didn't make a "true effort" to unify the party after the primary, according to the New York Post. 

And Sanders recently addressed criticism of his surrogates during the 2016 race, sending a new letter obtained by HuffPost that says he opposes "bullying and harassment" and warns surrogates against talking about "past grievances." 

Again, it's unclear how prevalent feelings of resentment are among Democratic primary voters that will actually decide the nomination. But the constant reminders of the 2016 election certainly won't help a party that wants to put that contest in the rear-view mirror, and could complicate the terrain for Sanders in the process.