WASHINGTON - Lawmakers of US Democratic Party are turning their fire on Senator Bernie Sanders, a left-wing politician seeking presidential nomination, as he marches toward a big win in Tuesday’s New Hampshire primary.

Congressman Gerry Connolly, a Democrat who supports Hillary Clinton, the party's front-runner, warned that Sanders could drag down Democratic candidates running for the House and Senate if he wins the nomination.

“I believe it could have real serious down-ballot consequences,” Connolly told The Hill, which covers Congress.

Congressman Scott Peters,  a Democrat who is one of the biggest Republican targets in the 2016 election cycle, suggested his constituents would view Sanders, a self-described Democratic socialist, as too extreme. “I’m not comfortable with it at all,” Peters, who has endorsed Clinton, said of the prospect of Sanders heading the ticket.

“He certainly wouldn’t match my district very well,” Peters added. “People in my district are looking for pragmatic, problem-solving leaders and he would not fit that bill. Some on the Republican side, I think, would be equally objectionable to my district as well.”

Other pro-Clinton Democrats dismiss Sanders’s leadership credentials, with that criticism coming even from members of the clubby Senate. Sanders is a great advocate, those Democrats say, but not nearly as qualified as Clinton to serve as commander in chief.

“Bernie has been here for 25 years. Lots and lots of people in Congress know Bernie well. We like Bernie, we admire Bernie. But of the almost 200 members of Congress who are Democrats, I think two of them have endorsed Bernie Sanders,” said Senator Claire McCaskill, a Democrat who is also a Clinton booster.

“This is about leadership. It’s about who can bring people together and accomplish the things we all want.

McCaskill said congressional Democrats don’t have much faith in Sanders’s ability to get things done if elected president “because he’s not been able to move the needle in 25 years in Congress.”

Such comments have generated strong pushback from Sanders allies on Capitol Hill, who accuse their Democratic colleagues of using scare tactics.

“Campaign operatives of hers and some surrogates continue to promote the attitude that we should be dismissive. That it can’t be done. That he’s not qualified,” said Rep. Raúl Grijalva, who has endorsed Sanders.

He said McCaskill’s approach “evokes the ghost of [former Wisconsin Sen. Joseph] McCarthy .” “It’s red-baiting and you’ll probably see more of that unfortunately, but I don’t think it’s going to stick.”

When asked about Grijalva's comments, McCaskill emphasized that she likes Sanders personally.

"I love Bernie, and the values that he and Hillary share are so important to all Americans, that electability really matters," she said.

Grijalva and Congressman Keith Ellison, the only Muslim lawmaker,  are the only two Democrats in Congress to have endorsed Sanders. They are the co-chairmen of the Progressive Caucus.

Clinton, meanwhile, has won the support of 150 out of 188 House Democrats and 39 out of 46 Senate Democrats, according to a tally kept by The Hill.

The sniping between the two presidential camps has raised fears of a nasty primary battle that could drag on until the Democratic convention, which is scheduled for the end of July in Philadelphia.

Democrats are worried because “the mean-ness of the attacks back and forth has gone up,” one Democratic senator said Thursday.

“Is this going to play out all the way until the convention? That’s what Secretary Clinton did in 2008. She went all the way until June against Obama,” the lawmaker said. “If Bernie does the same thing, you know, these attacks keep escalating.”

Sanders has vowed to fight to the end, and is making good on his promise by leaving behind a staffer in Iowa to fight for every delegate. "We are in this for the long haul," Sanders said just before the caucuses began Monday night.

For supporters of Clinton, her razor-thin victory in the Iowa caucuses Monday night has created fresh anxiety about her ability to avoid a prolonged fight with Sanders.

While the consensus among Democrats supporting Clinton is that she’ll perform better in the primaries after New Hampshire, they’re not sitting back and waiting for their campaign to catch fire.

Instead, they’re sharply questioning Sanders’s electability and leadership qualifications.

“I think Bernie’s terrific as an advocate. There’s a difference between a strong community advocate and being someone who can get things done,” said Sen. Debbie Stabenow (D-Mich.), who has campaigned extensively for Clinton.

McCaskill said Republicans are chomping at the bit to run against Sanders. “The Republicans won’t touch him because they can’t wait to run an ad with a hammer and sickle,” she told the New York Times.

Such rhetoric against Sanders has angered his supporters.

Ellison said Republicans would unload vicious attacks on the Democratic nominee no matter who it is. “That kind of thinking presupposes that they’re not going to try to rip the skin off of any Democratic nominee. I don’t know when us Dems are going to figure out the Republicans are trying to beat us,” he said. “The day will never come when the Republicans will say, ‘You know what? Your Democratic presidential nominee is just fine.’ ”

Ellison flipped the argument of Clinton allies that Sanders is not practical by praising his willingness to stick to principle.

He said Clinton has far many more endorsements because her campaign made it a high priority to collect them early.

With polls showing Sanders enjoying a 2-1 lead over Clinton in New Hampshire, some Democrats are beginning to wonder what it would mean if he won the race.

Congressman Jerry Nadler, a Democrat, who represents a reliably liberal Manhattan district, said a Sanders nomination could provide a “fresh face” for the party — or result in utter disaster.