GRAND RAPIDS, Mich. — Four years ago, Bernie Sanders scored a surprise victory over Hillary Clinton in Michigan's Democratic primary, a win that resurrected his insurgent candidacy after a string of Super Tuesday losses led many to write off his campaign for dead.

On Sunday afternoon, the senator from Vermont returned to the city that helped him do it: Grand Rapids, a longtime Republican stronghold where Gerald Ford was raised and where Democrats have started to make inroads, thanks to an influx of younger, more diverse voters.

In 2016, Sanders won Kent County, where Grand Rapids is located, by 25 points, one of his widest margins of victory in the state. But it was what happened next that many people around here still talk about: That November, Donald Trump defeated Clinton by just three points in Kent County, a surprisingly close victory in an area dominated by moderate Republicans who were openly skeptical of Trump.

Like other party officials across the state, local Democrats blamed lower-than-expected voter turnout and complained of how little time Clinton had spent campaigning in the region compared with Trump. His last stop as the GOP nominee was an after-midnight rally on Election Day in Grand Rapids that attracted thousands of people, one of two last-minute visits he made to the city in the final days of the campaign.

Around town, there were rumors that many Sanders supporters helped propel Trump to victory, voting for him or not at all in the general election — a trend that seemed to be partly confirmed by a 2017 Harvard study that found 8 percent of Sanders supporters in Michigan voted for Trump, enough to help him claim a surprise victory.

As Sanders rallied on a breezy Sunday afternoon ahead of what could be a make-or-break primary for his 2020 campaign, supporters said they felt a sense of deja vu.

Once again, Sanders was attracting bigger crowds and out-organizing a rival candidate in the area – this time, former vice president Joe Biden, whose struggling candidacy has been revived in recent days by big wins in South Carolina and in Super Tuesday states, after the party’s moderate wing united behind his candidacy.

“It’s the same forces that got Hillary on the ticket in 2016 that are at work now because they are scared of Bernie,” said Marsha Reeves, 71, who had driven to rally from nearby Newaygo, a conservative-leaning area north of Grand Rapids. “They’re doing everything under the radar that they can to make him look unelectable.”

“But look at the people here,” Reeves added, motioning around to an estimated crowd of roughly 7,000 who had gathered to hear Sanders speak in a parking lot in the middle of downtown, not including an overflow crowd of hundreds more who looked on from nearby streets and grassy areas.

“He is definitely electable. . . . He’s electable if people just have faith and vote for him.”

Sanders is still popular in the region. Though there are noticeably fewer campaign signs than four years ago, many cars still have “Bernie” bumper stickers, and many in the crowd Sunday turned out in vintage Sanders shirts from 2016.

But he faces a more challenging political environment than when he ran against Clinton, who was deeply unpopular in this part of the state.

Trump’s election sparked a rise in Democratic activism in the area, and that, combined with the region’s changing demographics, especially in the Grand Rapids suburbs, helped Democrats win several state and local races in 2018. Among them was Democrat Gretchen Whitmer, who defeated a Trump-backed candidate in the governor’s race. She was the first Democratic gubernatorial candidate in 32 years to carry Kent County, winning by nearly 12,000 votes

In 2016, Trump defeated Clinton by just over 9,000 votes.

“All evidence points to that we are becoming bluer,” said Gary Stark, chairman of the Kent County Democratic Party. “Things are changing politically.”

Those changes — especially what local officials say is a rise in activism among suburban women and college-educated white voters — would appear to favor Biden, who has won support from those groups in other early states.

But it hasn’t gone unnoticed by some local Democrats, even those not supporting Sanders, that Biden has done little campaigning in the area. The former vice president had a sparse campaign footprint in Michigan until recently, doing much of his organizing out of Detroit, which has a larger base of Democrats than Western Michigan.

After campaigning in other states, including Missouri and Mississippi, Biden held his first event in the state on Monday morning, a stop at a health clinic in Grand Rapids, to underscore his push for an expansion of the Affordable Care Act. Local news stations had touted Biden’s visit for days, only to announce Sunday night that this event would be closed to the public.

Although many believe Biden will do well in the area on Tuesday, some local Democrats privately fretted about what this means for a region that will almost certainly be a battleground in the fall. Trump, who personally fixated on winning Grand Rapids and Michigan in 2016, has visited several times since winning the presidency, including as part of his “thank you” tour in the aftermath of the 2016 election and again last year after the Mueller report had been released.

“Yes, [Biden has] done well in states where he hasn’t campaigned much or had an organization,” said one local Democrat, who declined to be named so as not to alienate the Biden campaign. “But I worry that he has not learned the lesson of Hillary Clinton, that Western Michigan is important and you need to be here to win.”

And Sanders’s rallies here in recent days have also raised questions about how the former vice president could even begin to win over voters who are a part of Bernie’s movement.

The Biden campaign and other Democrats have argued that the party will unite behind whoever is the nominee as part of a shared mission to remove Trump from office. But it’s not so clear that will work with some Sanders supporters.

Both in Detroit and in Grand Rapids, several young voters carried handmade signs that read, “Please don’t make me vote for Joe Biden.” They waved them even as Sanders, from the stage, vowed to support whoever is the Democratic nominee and campaign against Trump.

But it raised painful memories for many who turned out to hear Sanders in Grand Rapids, including Reeves. “I held my nose and voted for Hillary, even though I didn’t want to,” she said. She said she would do the same in 2020, adding that “absolutely anyone is better than Trump.” But she wondered if other Sanders supporters would feel the same and whether the excitement that Sanders has generated would be there for anyone else.

Her friend Sally Kane, who also supported Sanders in 2016 and ultimately voted for Clinton, recalled canvassing parts of their Republican-leaning county in the final months of the 2016 campaign.

“People were so dispirited, so disillusioned, so disenfranchised. They wondered why it was even worth it to vote because they felt the government had never done anything for them,” she recalled. Some of those people had ultimately backed Trump. “Those are the people that Bernie can get because he’s promising real fundamental change,” she argued.

Asked what Biden could do to win over those in the Sanders movement, both women shrugged. “Maybe at least try,” Reeves said.

Onstage, Sanders brought out the Rev. Jesse Jackson, the longtime civil rights activist who mounted his own insurgent bid for the Democratic nomination in 1988, when he upset Gov. Michael Dukakis in Michigan’s primary. He urged Sanders supporters to stay hopeful about the senator’s campaign.

“If you vote as you rally, we will win,” Jackson said.