WASHINGTON — Senate Democrats, who have worked more closely with Sen. Bernie Sanders, I-Vt., than anyone else the past 13 years, split into several factions when they consider the increasing likelihood of the self-proclaimed democratic socialist as their standard-bearer against President Donald Trump.

Some question whether Sanders can appeal to key suburban swing voters critical to the party’s hopes of claiming GOP Senate seats in Colorado, Maine, Arizona and North Carolina with such a liberal agenda. “I think winning a primary election and winning a general election are two different things,” said Sen. Michael Bennet, D-Colo., who had run for the 2020 presidential nomination himself.

Others say the key is forging unity once the presidential primary contest is settled, bringing together all sides to help Democratic chances up and down the ballot. “I’m not in the freakout caucus,” said Sen. Chris Van Hollen of Maryland, who has chaired House and Senate campaign committees. “I think the main thing is that we need to come together and support the eventual nominee, whoever that nominee is.”

Still others just avoid the topic. “I’m supporting whoever the Democratic candidate for president is,” said Sen. Gary Peters of Michigan, one of the few Democrats running a tough reelection campaign this year.

Sanders arrived in the Senate in 2007 after 16 years in the House, an iconoclast with big ideas and not a lot of legislative gravitas. He was neither loathed nor loved.

Then, in April 2015, Sanders went to the northeastern corner of the Capitol lawn, and with no supporters around and just a few staff members, announced his long-shot bid for the Democratic presidential nomination against Hillary Clinton.

Five years later, Sanders, who is not a registered Democrat, is easily the most well-known member of the Senate caucus, pledging a “revolution” that has vaulted him to the top of the 2020 field and left his colleagues wondering what comes next.

Officially, the mantra for Senate candidates is to stick to the 2018 campaign themes that House Democrats used to win the majority, focusing on pocketbook issues such as the cost of health care and prescription drugs while promising a corruption-free government.

“If you’re in your state and you’re talking to constituents about those kitchen-table issues that matter to them, that’s what they’re going to remember when they go to vote,” Sen. Catherine Cortez Masto of Nevada, chairwoman of the Democratic Senatorial Campaign Committee, said in an interview Tuesday.

Cortez Masto, whose home state delivered Sanders an overwhelming caucus win on Saturday, cited her experience in 2016 as she ran and won in a state that also was hotly contested in the Clinton-Trump race. “So yes, there is a presidential [race] going on, but at the end of the day, [voters] are going to be able to see you, because you’re going to be able to spend more time in your state,” she said.

Yet most senators and analysts understand how closely Senate races can track with presidential races. In Nevada, for example, Clinton and Cortez Masto both won by exactly 2.4 percentage points.

Bennet, a moderate, struggled to raise money in the Democratic primary and quit the race this month after finishing with less than 1% in New Hampshire. He ran the senatorial campaign committee in 2014, when President Barack Obama’s low approval rating contributed to a nine-seat loss for Democrats.

Heading into the 2020 primaries, Bennet said he hoped for a presidential nominee who could lift Democrats to a big Senate majority to pass some of the more sweeping legislative proposals. He paused for 17 seconds on Monday evening when asked about the potential of a Sanders nomination.

“We need to nominate somebody in this process who is going to be able to win purple states like Colorado and lead us to a 55-senator majority in the Senate. That could be challenging,” he said.

Part of the issue comes from Sanders’ proposals, such as Medicare-for-all, with multitrillion-dollar price tags. He has 14 co-sponsors for that proposal.

Sanders’ past includes controversial statements about socialist leaders, some of which were re-aired in Sunday’s “60 Minutes” episode when, during an interview last week, he applauded Fidel Castro’s literacy programs in Cuba.

“Listen, I’m sure that all of those political prisoners languishing in Castro’s jails, I’m sure all of those who were shot on a firing squad, I’m sure all of those who were tortured and live in New Jersey and can tell you their stories, would find the literacy program to really be worthy of losing all of their freedoms and all of their rights,” Sen. Robert Menendez of New Jersey, the only Cuban American in the Democratic caucus, said Monday night.

Menendez said Sanders made a mistake that would hurt him in the campaign. “It would definitely affect the race in terms of what people think,” said Menendez, who ran the 2010 senatorial campaign committee.

But many Senate Democrats think that, if he runs a disciplined and unified campaign, Sanders, 78, can win. “I think that whoever the nominee is, the race is going to be about Trump betraying workers, and it can work for any number of Democrats,” Sen. Sherrod Brown, D-Ohio, said.

“We have a lot of great candidates, including a good number of my senator friends,” Senate Minority Leader Chuck Schumer, D-N.Y., said. “I think every one of them will beat Trump.”

Sanders, as he did at Tuesday’s debate in Charleston, South Carolina, is fond of mentioning polls showing him ahead of Trump nationally and in several of the key Midwestern battleground states.

But a couple of hours before the debate, Van Hollen noted that Democrats need unity above all else. “The thing I really want to hear tonight, after people talk about their disagreements, is each of them pledging to support 100% the nominee,” he said.

However, the debate often devolved into a shouting match as the candidates talked over one another and took personal shots.

For now, some Democrats are planning their own campaigns regardless of who is at the top of the ticket.

An underappreciated politician, Peters defeated a 16-year veteran House Republican in 2008, won reelection two years later in a brutal political climate and won his Senate seat in the tough 2014 season.

“I’ve always been able to run above the Democratic base. I run my own race based on my own issues. So whoever the Democratic candidate is, I’ll be supporting,” he said.