Mark Stewart, frustrated with Hillary Clinton and Bernie Sanders, launches upstart 2016 bid

Mark Stewart is frustrated with the Democratic Party.

A registered Democrat who identifies as libertarian, Mr. Stewart wonders where all the more fiscally minded Democrats have gone.

“JFK wouldn’t be a Democrat today,” Mr. Stewart said. “The party — or at least the leadership — has moved so far left from where they were in the ’60s or ’80s, we’ve now got three socialists running for president.”

So Mr. Stewart decided to do something about it: He was the first person to register for the New Hampshire presidential ballot, and is waging a long shot campaign for the Democratic presidential nomination, hoping at the very least to try to wake the party up.

“I’d love for one reporter to ask one of the current leaders of the progressives, why do they consider themselves a Democrat?” Mr. Stewart challenged. “Who was one of the biggest advocates for work, saying if you can work, you ought to work? That was Bill Clinton. Where has this mindset gone?”

The two front-runners of the Democratic presidential primary are Hillary Clinton, widely viewed as a member of the professional political class, and Vermont Sen. Bernard Sanders, a self-described socialist. Mr. Sanders has arguably pushed Mrs. Clinton further to the left on economic issues she once supported but no longer does, like the Trans-Pacific Partnership. She’s also proposed “debt-free” college tuition and a number of social initiatives, like giving caregivers tax credits, without indicating how they would be paid for.

In an interview this week on MSNBC’s “Hardball,” Mrs. Clinton was pressed to identify the difference between a Democrat and a socialist by host Chris Matthews, to which she responded: “I am a progressive Democrat who likes to get things done.”

Democratic National Committee Chairwoman Debbie Wasserman Schultz also failed to differentiate between socialists and Democrats on Mr. Matthews’ show, leaving Mr. Stewart to wonder whether there are any moderate Democrats left.

He’s not alone.

Jim Webb, the former senator from Virginia, dropped out of the Democratic presidential race in October, saying the party had drifted too far from its traditional messaging.

He’s now pondering a third-party run at the White House, and on Thursday he retained the services of Sam Jones, the national finance director for the past effort to draft Vice President Joseph R. Biden into the race.

“After weeks of study, including consultations with ballot experts and independent activists around the country, we have a handle on what it takes to give voters in every state a real choice,” said Webb spokesman Craig Crawford.

The shrinking pool of moderate Democrats is visible on Capitol Hill, where Blue Dog Democrats — that is, Democrats who are more fiscally conservative on issues such as budget deficits and business regulations — were one of the most influential voting blocs in Congress just five years ago.

But the Blue Dog Coalition has seen its numbers slashed from more than 50 to just 15 after the 2014 elections.

Part of the change has been the voters themselves.

According to a comparison of news polling conducted by The Wall Street Journal and NBC News from 1990 to 2015, the demographics and beliefs of both parties — Democrat and Republican — have changed significantly over the years. In 1990 13 percent of Democrats considered themselves “very liberal,” compared with 26 percent in 2015. On the opposite measure, 21 percent of Democrats in 1990 said they were either “somewhat conservative” or “very conservative,” compared with only 10 percent last year.

Meanwhile, Democrats have seen their hold on blue-collar workers slip — 44 percent of blue-collar workers now identify as Republican — as the party wins a higher share of the rich, according to The Wall Street Journal.

That shift has not been lost on members of the party, especially those who don’t support the socialism of Mr. Sanders or the elitism of Mrs. Clinton.

“Clinton seems more scripted, making it tougher for her [than her husband Bill Clinton] to have personal connections,” said John Colombo, the chairman of the Franklin County Democrats in Iowa. “She’s been campaigning for this for like nine or 10 years now. With Clinton you have 100 percent name recognition and people know what they’re going to get: a politician.”

With Mr. Sanders, on the other hand, “It’s all about Wall Street billionaires and support for low-income people. The younger people that are supporting him, well they’re not yet in a position where you could call them extremely successful, so it resonates with them,” Mr. Colombo said. “I don’t think he has a bad message, but it’s very narrow.”

Larry Hodgden, another moderate Democrat in Iowa, agrees.

“Hillary Clinton, for all of her strengths and experience, and counting the fact that Bill was really a great Democratic president, she’s a lightning rod, and Republicans will never get off her case,” Mr. Hodgden said. “That will stifle and cause problems for us as a country to move forward.”

Mr. Sanders, meanwhile, hasn’t shown he can handle all parts of the job as president, said Mr. Hodgden, the chairman of the Cedar County Democrats in Iowa.

“Sanders is a great motivator, a progressive thinker, but I don’t see him as commander in chief. He lacks some of the experiences he needs to do that,” Mr. Hodgden said.

Mr. Stewart, and perhaps Mr. Webb, are hoping there are enough moderate Democrats left to rally.

“In New Hampshire the Democratic Party has stopped saying ’Jefferson-Jackson’ dinner; they now call it the ’JJ dinner’ because it’s no longer politically correct to be associated with Jefferson as a Democrat,” Mr. Stewart said. “They’re afraid of what he stood for.

“To me, that’s nonsense. So for all the Democrats who are stuck with the choice between Bernie and Hillary, how about punking them a little bit with a vote for Mark?”

Mr. Stewart, who is a graduate of Dartmouth College and is an entrepreneur, is on the ballot in Georgia and New Hampshire, and is working on getting the signatures he needs to qualify for Vermont. He also says he’s looking to make a play in the Colorado caucus, where you don’t have to formerly register to become a candidate.