House Democrats facing tough reelection battles this fall are growing concerned about the early presidential primary success of socialist Bernie Sanders, fearing it could imperil their chances.

The Vermont senator, 78, narrowly won the New Hampshire primary Tuesday, on the heels of a close second-place finish in the Iowa caucuses, a result his campaign disputes due to protracted vote-counting problems. At the same time, 29 House Democrats are seeking another term in districts President Trump won in 2016.

Sanders's advocacy of far-left causes, including "Medicare for all" and what he calls free college, may not play well in dozens of swing districts, particularly his ready admission that he's not a capitalist.

“I have respect for Senator Sanders, and I believe that he could probably win the popular vote. But do I think that he would win the five or six states that matter in this election and, certainly, keeping the districts that we fought so hard to win for the first time in generations, in some cases?" said Rep. Dean Phillips, a first-term Minnesota Democrat and supporter of Minnesota Sen. Amy Klobuchar's presidential bid.

"I think this would be a great challenge and a potential consequence,” Phillips told the Washington Examiner when asked about Sanders's rise in the Democratic presidential primary field.

Rep. Elissa Slotkin, a first-term Michigan Democrat, represents a district that was won by Trump by a margin of 6.7 points in 2016. She says the primary campaign is still in its early stages.

“Obviously, we're going to watch what's happening in the next couple of races. For me, I think most people are still trying to decide what to do. A lot of Michiganders have had their absentee ballots since late January,” Slotkin told the Washington Examiner. “And I think there's still a lot of debate about who to vote for and where to go forward.”

Rep. Alexandria Ocasio-Cortez, a New York Democrat and vocal Sanders supporter, told reporters Wednesday that no matter who ends up the nominee, Democrats will unify behind the candidate.

“There will always be concerns about party unity, no matter who it is. If Klobuchar or whomever was the front-runner right now, there would be a lot of stress as to whether progressives would unify," she said.

On the other side of the Capitol, Sen. Gary Peters, a Michigan Democrat, is in a potentially tight reelection campaign against Republican challenger John James.

Trump won Michigan in 2016 by 0.23%, which, along with narrow victories in Pennsylvania and Michigan, made him president. Peters told the Washington Examiner he plans to support whoever the Democrats end up nominating at their convention when asked about Sanders’s surging support as the current front-runner in the first two primary contests.

“When I run my race, I run my race, and I'll run with whoever the Democratic nominee,” Peters said.