Returning to Iowa for the first time in a week after being stuck in Washington for the impeachment trial, Sanders told voters his campaign team had built the strongest field organization in Iowa. But he said if he did not win the nomination, the Democratic Party will still be unified.

“Certainly I hope that we’re going to win. But if we do not win, we will support the winner, and I know that every other candidate will do the same. We are united in understanding that we must defeat Donald Trump,” Sanders said Saturday.

His comments seemed to be an effort to get past old wounds from the 2016 campaign, when the former Secretary of State and her allies criticized Sanders for what they perceived as a lack of enthusiasm in uniting Democratic voters ahead of the general election.

Clinton herself has ripped open those healing scars in recent days.

In a podcast released Friday , Clinton blamed “a lot of people highly identified with [Sanders’s] campaign” for urging Sanders supporters to vote for third party candidates in 2016, or to simply sit the election out.

“It had an impact,” Clinton told Emily Tisch Sussman, a Democratic strategist who hosts the podcast, "Your Primary Playlist." “Unfortunately, you know, his campaign and his principle supporters were just very difficult and really, constantly not just attacking me, but my supporters.”

Clinton’s comments came just a week after a new documentary set to debut at the Sundance Film Festival ripped open old wounds. In an interview for the documentary, Clinton said “nobody likes” Sanders, renewing raw emotions that have lurked below the surface since Clinton lost her bid to become the first woman in the White House.

Sanders backers said they would back the eventual Democratic nominee, even if it wasn't the Vermont independent. But several said they were frustrated that Clinton had once again inserted herself in a race in which she is not a candidate.

“It kind of feels back-stabby,” said Daniel Hyer, of Columbus, Ohio, who drove 11 hours to Iowa to work as a precinct captain for Sanders. “I know he worked really hard for her after the end of the convention.”

“It’s just stupid,” said Dian Curran, a Sanders volunteer and research scientist who runs a chicken farm in rural Warren County, about Clinton’s comments.

“I’m very irritated with the Bernie supporters and the way they behaved towards Hillary and wouldn’t vote for her. It’s one of the reasons we have Trump today. So I have no time for Bernie,” Morris said. “I think he’s a lot of hot air with good intentions. He’s accomplished very little in all the years he’s been in the Senate. He’s not a good compromiser. He doesn’t know how to get things done. I think his time has come and gone.”

Sanders lost the Iowa caucuses to Clinton by a small margin in 2016, but this year he has built what Iowa Democrats say is a stronger campaign team.

Misty Rebik, Sanders’s Iowa campaign director, said his organization would have at least one precinct captain in every caucus location in the state — and, in some larger precincts, several captains to corral voters. Those volunteers go through as many as four levels of training. Sanders said Saturday that the campaign had knocked on half a million Iowa doors since the beginning of January.

“The caucus is all about organizing, and we’ve taken organizing very seriously, I think more seriously than any other candidate in the state,” Rebik told The Hill. “We’ve been doing unique organizing that I have never seen any other presidential candidate do.”

At the same time, veteran Iowa Democrats who back other candidates are increasingly voicing their concern about polls that show Sanders leading the field.

Sanders answers critics who say he cannot appeal to moderate voters in key Midwestern states by pointing to the new voters he would draw into the electorate.

“To defeat Donald Trump, who will be a very formidable opponent for a number of reasons, we need to have the largest voter turnout in American history. That’s just a fact. If it is a low turnout election, Trump will win,” Sanders said Saturday. “And I believe that our campaign is the campaign of energy, is the campaign of excitement, is the campaign that can bring millions of people into the political process who normally do not vote.”