If the socialist left -- not long ago considered a fringe movement -- seems as if it’s lately been bargaining from a position of power, it might be due to a recent flood of support: since 2016, the ranks of the Democratic Socialists of America (DSA) have swelled from 6,000 to over 45,000 dues-paying members.

“Our members are not interested in half-measures.” - Maria Svart, Democratic Socialists of America

Asked whom the DSA would endorse in the 2020 presidential election, Maria Svart, its national director, told ABC News that she can't predict which candidate the group will support -- members vote democratically on endorsements -- but she doubts her organization would back a candidate any less ardently leftist than Sen. Bernie Sanders, himself a Democratic Socialist.

“Our members are not interested in half-measures,” Svart told ABC News.

Her uncompromising stance contrasts sharply with the more moderate base of the Democratic party, which, some Democratic leaders say, is eager to rally around a candidate who stands a better chance against President Trump.

Matt Bennett, senior vice president of center-left think tank Third Way, told ABC News he thinks a "happy warrior, someone who is unafraid to stand up directly to Trump, to hit him square in the nose" would be "the best bet for the party going forward."

But when it comes to which candidate Third Way will support for president, "the real answer is, whoever is nominated to run against Trump," Bennett said. “We’ll work with anyone who wants to work with us.”

Bennett's Third Way represents the more moderate flank of the 2018 Democratic Party, which has found itself split as a socialist-leaning left wing scores electoral victories and begins to build a coalition.

The DSA's member surge began during the 2016 presidential race, and spiked again when card-carrying Democratic Socialist Alexandria Ocasio-Cortez scored an upset victory over Democratic party heavyweight Joe Crowley in New York.

On the heels of Ocasio-Cortez’s win, she and other Democratic Socialists have thrust left-wing proposals into the spotlight, turning a push to abolish the U.S. Immigration and Customs Enforcement agency (ICE) from a Twitter hashtag into proposed legislation and popularizing bold economic demands like Medicare for All.

As socialists move into the mainstream of political discourse, Democrats and political heavyweights have wrestled with how to respond.

The ‘socialist left’ wouldn’t appeal to ‘America’s great middle,’ former FBI director James Comey wrote on Twitter. “Democrats, please, please don’t lose your minds and rush to the socialist left,” he cautioned.

Beyond ideological differences with Democrats, however, DSA members argue that tailoring progressive proposals to be more politically-palatable makes for poor electoral strategy.

“Democrats argue that they’re concerned about electability in the coming election, but the reality is, they failed in 2016, and 46 percent of people don’t bother to vote,” Svart told ABC News.

Many leftists argue that truly purple ‘swing voters’ are few and far between, and believe that in order to flip districts, the left should focus on Americans disillusioned with politics as usual.

Moderate Democrats remain skeptical of the DSA’s radicalism, however, arguing that too many leftist proposals are just political non-starters.

Gearing up for midterms, Democrats re-branded on bread-and-butter issues

When Democrats unveiled their messaging re-brand in 2017, economic concerns were front and center.

"President Trump campaigned on a populist platform, talking to working people," Sen. Chuck Schumer told ABC News in an interview on the new platform. ". That's why he won."

“The No. 1 thing we did wrong is not present a strong, bold economic agenda to working Americans,” he said.

Though the party has converged on messaging geared toward working Americans, many DSA members doubt that Democrats share their vision for radical economic populism.

Democratic party leaders tout economic populism as a ‘big tent’ strategy -- one that includes wealthy urban professionals alongside union workers -- whereas the DSA defines its economic populism not only according to whom it attracts, but whom it excludes: socialists are not only for the working class, but explicitly pitted against the ruling class.

“Socialists view the world as being divided between two fundamental groups of actors: people who work, and people who get the credit for the work of others,” Svart told ABC News.

A growing movement to reject corporate campaign funding, led by progressive organizations such as Justice Democrats and Brand New Congress (both groups that backed Ocasio-Cortez), also stresses that the aim is not only ensuring particular candidates aren’t beholden to individual corporations, but building broad-based resistance to the donor class.

Democrats have increasingly adopted left-wing rhetoric in discussing economic proposals -- in the same interview on The Week, Schumer repeatedly invoked a classic Bernie Sanders-ism, “the system is rigged.” But Schumer and other party leaders steer clear of terms like ‘ruling class,’ more often designating the Trump administration as progressives’ common adversary.

‘Identity politics’ includes class identity

In 2016, then-candidate Bernie Sanders predicted that disagreement in the Democratic Party over “whether we go beyond identity politics” would deepen and become fault lines on the left.

“It is not good enough for somebody to say, 'I'm a woman, vote for me’... What we need is a woman who has the guts to stand up to Wall Street, to the insurance companies, to the drug companies, to the fossil fuel industry,” Sanders said on WBUR.

“It is not good enough for somebody to say, 'I'm a woman, vote for me...’" - Sen. Bernie Sanders

Sanders anticipated a concern increasingly voiced on the left: candidates might rely on belonging to an underrepresented identity group in order to vie for the progressive vote, without advancing a truly left-wing platform.

Svart pointed to President Barack Obama and Hillary Clinton as examples of politicians who only tenuously support the identity-based interests they claim to represent. Clinton campaigned as a feminist but did little to advocate for working-class women, Svart said, while Obama was nicknamed “deporter-in-chief” by immigration advocates who had once hoped the former president’s race would make him a natural ally.

On this view, Democrats’ deliberation over whether to focus on recapturing the vote of the ‘white working class’ or focus on attracting groups such as African-American, Latino or LGBTQ voters turns out to be a false choice. Democratic Socialists argue that a platform of radical economic justice proposals would galvanize a diverse coalition of Americans over shared economic interests -- a more promising electoral strategy than the lukewarm pluralism invoked to corral a “big tent.”

‘Faux progressives’

Svart told ABC News that since Ocasio-Cortez’s victory, she has noticed more “faux progressive” candidates invoking left-wing rhetoric but lacking sufficiently radical platforms.

"Our base cares about policy, not platitudes." - Maria Svart, Democratic Socialists of America

“Politicians are opportunists, and organizers are also opportunists," she said. "So, people wanting to adopt the name Democratic Socialist or talk about Medicare-for-All simply means that they’ve recognized that there is a base behind it."

“To me," she said, "that means that we’ve been successful in building something that people want access to. But of course people are going to try to co-opt it – that’s the way politics works.”

Svart cautioned progressives contemplating running on the left: “We welcome it, but they should remember that our base cares about policy, not platitudes.”

This is not a new concern for the DSA, which has long been skeptical of having its radical proposals co-opted by mainstream politics.

However, Svart says that as the organization gains new attention Democratic Socialists have doubled down on remaining bold and uncompromising, emphasizing political education and worker organizing at local chapters.

“We have a vision which is broader than just electoral politics; we believe in building a working-class movement. It’s not just about election cycles, it’s about asserting your rights collectively, and that’s the only way we can prevent things from being watered down,” Svart said.

Contingent alliance with Congressional Progressive Caucus

The DSA is not a monolith and local chapters see spirited disagreement over both theory and strategy, but Democratic Socialists ultimately envision an end to capitalism, which they critique as fundamentally crisis-prone and unjust.

In the short run, they are pursuing a platform that has been erroneously equated with New Deal or Great Society liberalism. Although Democratic Socialists push for union organizing, scaled-up social benefits and universal health care, they also insist that welfare state progressivism is ultimately insufficient.

“Socialists work for reforms that weaken the power of capital and enhance the power of working people, with the aim of winning further demands,” wrote Joseph M. Schwartz, vice-chair of the DSA, and Bhaskar Sunkara, founding editor of socialist magazine Jacobin. They noted that single-payer health care is a classic example of just such a “non-reformist reform.”

That is, even as socialists push for Medicare for All -- a proposal that has gained momentum since Sanders made it a key plank of his 2016 presidential run -- they see expanded Medicare as just the first step towards a fully-nationalized health care system that would more closely resemble something like the Swedish model or the British National Health Service.

Svart agreed that while progressive Democrats can serve as allies, the DSA is not in lockstep with coalitions like the Congressional Progressive Caucus (CPC) – the House bloc that recently put forth a bill to abolish ICE. The bill was quickly deemed too radical to even merit a vote.

“We are united superficially, but we have a very different analysis,” Svart said of the DSA’s shared ground with progressive Democrats like the CPC.

Ocasio-Cortez, who made abolishing ICE a key rallying point in her campaign, has suggested that a more hard line leftist caucus would be in order. In an interview on “The Dig,” a Jacobin podcast, she proposed carving out “a sub-caucus of the Progressive Caucus -- a smaller bloc, but one that operates as a bloc.”

The idea was touted by leftist publications as a potential counterweight to the ultra-conservative Freedom Caucus.

Meanwhile, while she praised recent efforts to abolish ICE, Svart noted that the DSA believes in razing the agency specifically because it is “a weapon of the ruling class to make working people afraid, and therefore more easy to exploit.”

She doubts that most progressive lawmakers would agree with that framing.