WASHINGTON — While congressional Democrats share in their party's overriding goal of defeating President Donald Trump in November, there is growing concern that their efforts to retain a somewhat fragile House majority and hopes of winning control of the Senate could be hampered with Sen. Bernie Sanders, I-Vt., at the top of the ticket.

Democrats worry that Sanders, a self-described democratic socialist, and his policies are too liberal for the broader electorate they need to win in states and districts that Trump won in 2016.

In particular, they are concerned that having Sanders at the top of the ticket could drive away suburban voters who favored Democrats in the 2018 midterm elections in the nation's small number of closely divided districts and put potential Senate seats out of reach in GOP-leaning states.

Rep. Anthony Brindisi, D-N.Y., is among those who won close races less than two years ago, defeating incumbent Republican Claudia Tenney in New York's 22 Congressional District. “My preference would be to see a more moderate candidate at the top of the ticket — someone who reflects more of the districts that delivered the majority in 2018,” said Brindisi, who will face Tenney in a rematch in November. “And I don't think (Sanders) really represents that.”

Democrats captured the House majority in 2016 by winning a net of 41 seats, including races in 31 districts the president also carried in 2016.

As part of the effort to keep those seats, Democrats have put Rep. Cheri Bustos, D-Ill., who represents one of those 2016 Trump districts, in charge of the Democratic Congressional Campaign Committee, which is dedicated to winning House races. While the committee has been focused on keeping those suburban swing voters and broadening the party's appeal among them, many Democrats fear that Sanders’ uncompromising belief in large government programs, including "Medicare for All," and a wholesale change to the economic system will hinder their efforts, especially if the nation's overall economy continues to hum along.

House Speaker Nancy Pelosi, D-Calif., is fiercely protective of these members who chose her for the position a second time and sent a signal this week that an alternative presidential candidate, like former New York City Mayor Mike Bloomberg, would be better for winning down-ballot races.

“I think that his involvement in this campaign will be a positive one,” Pelosi said in a soft embrace of the one-time Republican mayor earlier this week.

On Thursday, however, she dismissed claims that Democrats are jittery about the presidential race. “We are calm, cool and collected,” Pelosi told reporters. “I mean, just because some people may be speaking out about not liking one candidate or another, that’s the democratic way, that's politics, it’s a messy business.”

Asked about concerns among Democrats on Thursday, Sanders told reporters on Capitol Hill that if Democrats are going to defeat Trump, "we're going to have to get young people a lot more involved in the political process" and "expand minority voting. And I think we have a campaign to do that."

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Still, it's a concern that Democratic strategist James Carville, who advised Bill Clinton in his successful 1992 presidential campaign, has been sharing on numerous cable television appearances in recent days.

If Sanders is the nominee, Carville said in an interview on MSNBC last week, "I’m gonna vote for him" and Democrats could retain control of the House. But, "18 percent of the United States elects 52 percent of the Senate."

"You know what’s going to change? Nothing. Bernie Sanders is president, Mitch McConnell majority leader, the Republicans control the federal courts. Come on, people, we got to have a big election here."

In order to win a majority in the Senate, Democrats need to gain a net number of four seats (or a net gain of three seats if a Democrat wins the White House), a tall order considering that most of the Republicans up for re-election hail from solidly Republican states.

Democrats are targeting a host of Republican incumbents in purple or blue states, particularly Sens. Cory Gardner of Colorado, Susan Collins of Maine, Martha McSally of Arizona, Joni Ernst of Iowa, and Thom Tillis of North Carolina.

But they also have seats they must defend, especially in Alabama where Sen. Doug Jones won a special election against a scandal-ridden Republican in 2017. And, a nightmare scenario, Democrats say, is for an unpopular presidential nominee to put other incumbents in danger, such as Sens. Gary Peters of Michigan or Tina Smith of Minnesota.

Sanders “may make it harder rather than easier for us to take back the Senate,” Sen. Chris Coons, D-Del., a close friend and supporter of former Vice President Joe Biden, warned.

The concern among Democrats has grown since Sanders walked away with a first place finish in New Hampshire and an apparent close second in Iowa. NBC News has not called a winner in Iowa.

While only two states have spoken in the long slog of the Democratic primary process, Sanders seems to be dominating the more progressive lane of the candidates while the more moderate candidates such as Sen. Amy Klobuchar, D-Minn., former South Bend, Indiana, Mayor Pete Buttigieg, and Biden, are splintering the rest of the vote.

In Minnesota, Trump lost by 1.5 percent, just over 44,000 votes, in 2016 and his campaign sees a path to win it in 2020. Smith, who is up for re-election, said that winning in Minnesota depends on the independent voters. She is supporting her home-state senator, Klobuchar, and insists that a unifying candidate is necessary to boost turnout, and a Democratic victory, in November.

“What we need, not only in Minnesota, is somebody that can bring people along up and down the ballot,” Smith said.

Many congressional Democrats think Biden and Bloomberg will resonate most with suburban voters, and they are registering those beliefs with endorsements. Biden has received 47 congressional endorsements so far, leading the field. Bloomberg, who has been in the race for only a few weeks, has the second most with 14 as of Thursday morning.

Sanders, who has served in the House and is a member of the Democratic leadership in the Senate received just eight endorsements from his colleagues.

Sen. Joe Manchin, D-W.Va., said the Democrats have “a lot of good” candidates running this year, naming the more moderate candidates Biden, Buttigieg and Klobuchar. While Trump won West Virginia by more than 40 points in 2016, Manchin thinks that Democrats can be competitive if they nominate the right candidate.

“I know my state is not going to go far left at all. Not liberal,” Manchin said.

Rep. Ro Khanna, D-Calif., a co-chair of the Sanders campaign, insists that Sanders can compile a winning coalition that turns out the voters that Democrats have been shedding, including rural voters and voters without college degrees.

“We need someone at the top of the ticket who's going to get record turnout and appeal to those demographics that we need to win back the presidency,” Khanna said.

Perhaps acknowledging that Sanders message won’t work in everyone’s district, Khanna said it’s up to members of Congress to “tailor their message for their districts,” regardless of who is at the top of the ticket.

Still, some Democrats think the party is overreacting.

“I'm gonna support whoever gets the nomination. That’s the most important. All these people stirring pots are stirring pots,” Rep. Debbie Dingell, D-Mich., said.