LA CROSSE, Wis. — Progressive insurgents Francesca Hong and Abdul El-Sayed want to shake up the next race for the White House — a notion that will likely petrify many top Democrats.Why it matters: They aren't running for president — they're vying for statewide office this year in presidential battlegrounds, and their campaigns are closely watched tests of the Bernie Sanders–style populism they want their party to embrace in 2028.It's a question that has haunted Democrats for a decade: Is America ready for a full-on left turn in politics, like what Sanders pitched when he ran for president in 2016?The prospect worries many old-guard Democrats who fear Hong and El-Sayed can't win a November general election.Driving the news: Hong, a self-described democratic socialist running for Wisconsin governor, is leading the polls for Tuesday's primary by double digits, as the party establishment tries to stop her. She told Axios during a get-out-the-vote tour that a win in November could boost progressive presidential hopefuls in the future."A victory for our campaign is a victory for working-class people in Wisconsin and across the country — and it could signal to many candidates that we have common issues that we can be fighting for," Hong said.El-Sayed, Michigan's new Democratic nominee for Senate, went further in a Politico interview, prodding prospective 2028 candidates to embrace Medicare for All and other pieces of his populist agenda."If not, I'm going to dog you up and down the state," he warned with a brash smile.Zoom in: Progressives have long argued that Democrats twice lost the White House to Donald Trump not because voters see them as too far left, as many moderates believe, but because they're viewed as champions of a broken status quo.We're beginning to get a glimpse of what testing that theory looks like — and how Republicans are adopting their own strategies in return.To put the challenge into context: No progressive as closely aligned with Sanders as El-Sayed has won a battleground Senate race — and the U.S. has never elected a socialist governor.There was something of a split screen this week in the way many Democratic insiders were responding to El-Sayed — whom many party leaders are slowly growing more comfortable with — and Hong, whom even several leading progressives are keeping at arm's length.El-Sayed, a former public health official who campaigned on abolishing ICE and expanding Medicare to all Americans, signaled a willingness to reassure general election voters about his views on immigration while also maintaining the pugilistic tone that helped him win a hard-fought primary."We can have a secure border, we can enforce immigration policy, but we can do it without shooting people in the face or the back of the head," he said at a rally Friday.El-Sayed embraces the left but eschews the "democratic socialist" label, even though several leading progressives who support him describe themselves that way.Many party bigwigs — mindful of Democrats' uphill fight to win control of the Senate — endorsed El-Sayed after his primary win in a show of unity.Hong's rollout onto the national political scene has been shakier.Hong is a restaurant owner-turned-state representative in Wisconsin whose shoestring campaign unexpectedly caught fire as she championed affordability and backed a moratorium on building data centers at a time when her opponents' campaigns were plagued by scandals.Milwaukee County Executive David Crowley is the chief Democratic candidate looking to stop her, backed backed by Wisconsin Gov. Tony Evers (D).As Hong has garnered national attention, she's gone viral for being mealymouthed when asked on CNN about a past social media post calling to "cancel Thanksgiving."Following her in Wisconsin, we saw signs she was adapting her message as voters asked her about her old posts at stop after stop."People care about the solutions, not just slogans and labels," she told us. Hong told Politico she had "some bad takes on Twitter," but "I've evolved, I've learned."She and El-Sayed have faced criticism over former comments supporting "defunding" the police, which they both have walked back — taking a page from New York City Mayor Zohran Mamdani's playbook.Friction point: Some Democratic strategists who think Hong is too far left are quick to point out that although progressive leaders Sanders and New York Rep. Alexandria Ocasio-Cortez have endorsed El-Sayed, they haven't backed Hong.Hong has brushed it off, telling Axios she hasn't sought their endorsements. She said she has had a brief conversation with the Democratic Governors Association.Asked about Hong on ABC, Ocasio-Cortez said Hong has "moved away" from past positions.Some D.C. Democrats are signaling they might be able to get on board. Senior DGA officials said Friday that they believe all of their party's primary candidates can defeat Rep. Tom Tiffany, the expected GOP nominee. They point to polls showing a tight race in November.The other side: Republicans are treating El-Sayed and Hong much the same, casting both as extreme and out of touch.During their respective primaries, GOP groups tried to prop up both candidates, suggesting Republicans preferred to run against them instead of more moderate Democrats.Reality check: Hong still needs to win her primary Tuesday. Crowley, who's seen a bump in the polls, is explicitly arguing that Hong would be a liability for Democrats in the fall."People don't like socialists," he told Axios. "Socialists didn't poll very good.… And so it's leading me to believe that she can't win."The bottom line: Hong and El-Sayed's success or failure could serve as a signal to Democratic primary voters as they weigh the electability of a progressive presidential candidate in 2028.AOC, who's considering a run for Senate or president, is sure to be watching.