A day after presidential rivals argued on the debate stage that Bernie Sanders' nomination would cost moderate Democrats their seats across the country, congressional Democrats began to echo similar concerns.

Rep. Kim Schrier, who flipped a Washington state district from red to blue in 2018, was asked whether Sanders at the top of the ticket could be devastating to down-ballot candidates in the House.

“This is a big-tent party and there is a lot of variety of viewpoints. And … there may be consequences,” said Schrier, the first pediatrician elected to congress.

Rep. Gil Cisneros, D-Calif., another swing district freshman, said he’ll support the Democratic nominee but declined to commit to campaigning on the same stage as Sanders when asked by reporters.

Democrat Gil Cisneros flipped a red seat in the 2018 midterm election.  (AP)

“We don't know who the nominee is going to be yet,” Cisneros said at the Capitol Wednesday.  “So you know, I think that's [thinking] too far into the future."

He added: "Whoever the Democratic nominee is... Democrats in my district are going to rally around that individual.”

Cisneros, a former Republican, said he’ll distinguish himself from the nominee on issues such as Medicare-for-All or free college if they don't align.

“I think people know where I stand and I've been pretty vocal in my district where I am on the issues and I think people will get behind me on that," he said.

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Privately Democrats in swing districts have been quietly freaking out about the possibility of a democratic socialist at the top of the ticket, Fox News previously reported. Several interviewed by Fox earlier this month warned that Democrats will lose the House if Sanders and his extreme policies are on the ballot in their moderate districts.

“It’s bad,” one freshman Democrat from a swing district said after Sanders’ New Hampshire win. “We are having conversations about how to deal with this.”

“If [Sanders] is the nominee, we lose,” another Democrat told Fox News at the time.

At the South Carolina debate, both former New York City Mayor Michael Bloomberg and former South Bend, Ind., Mayor Pete Buttigieg warned voters that a Sanders’ candidacy would cost Democrats down-ballot elections.

“It adds up to four more years of Donald Trump in the White House, Kevin McCarthy as Speaker, and an inability to get the Senate in Democratic hands,” Buttigieg said.

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Both Speaker Nancy Pelosi and Democratic Caucus Chairman Hakeem Jeffries made the case that the House will be firmly in Democrats’ hands and attempted to quiet the concerns.

Pelosi said Wednesday she’ll support Sanders at the top of the 2020 ticket and responded “no” when asked if his candidacy could cost the House Democratic majority.

Jeffries, from New York, said Democrats picked up “40 seats in a historic blue wave election” by running on the people’s agenda  -- lowering healthcare costs, increasing paychecks and working on infrastructure -- and voters will see House Democrats fulfilling those promises.

“I look forward to re-nominating Speaker Nancy D'Alesandro Pelosi on the floor of the United States House of Representatives in January 2021 and making it clear that House Democrats are still down with NDP,” Jeffries said Wednesday, in a nod to his famous nominating speech in 2019.

With his recent big win in Nevada and his strong finishes in Iowa and New Hampshire, a Sanders nomination is seeming increasingly possible. While some Democrats say it's still way too early in the nominating process, others are giving thought to how his nomination would affect their colleagues.

Rep. Joyce Beatty, D-Ohio, who is facing a progressive primary challenger, gave credit to the front-line House members in swing districts who have taken tough votes and argued they can’t afford to be attached to extremist ideas – whether they are from Sanders or anyone else.

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“If you're that radical, I don't care who you are, I think you put our members in jeopardy who are on the front line, and those folks, every day, come here and fight for the people against all odds, so I'm going to stand up with them because they're here for the people,” said Beatty, who hasn’t endorsed but thought former vice president Joe Biden “came into his own” on the stage in South Carolina, a must-win state for him.

Beatty also said questioned the math on Sanders’ sweeping proposals (“You have to be able to count”) and his ability to enact change if elected.

“Bernie Sanders has been here for almost 30 years, if this stuff was so great, why wouldn’t we have any of it now?" Beatty said.

She urged Sanders or any of senators who want to be president to take up one of the more than 400 bills that the House passed in the last year that now sit dormant in the Senate.

“My message to them is: Pass one of the bills that Speaker Pelosi sent over there," Beatty said. "And that's not just beat[ing] up on Bernie, that’s anybody that's over there now professing that they're going to do all the things that we've already done in the House. Words matter and you have to be able to count.”

Democrats will face their next big test Saturday when South Carolina voters head to the polls. Biden has staked his campaign on a comeback there.

Fox News' Caroline McKee contributed to this report.