Laura Hubka remembers experiencing a political conversion the first time she heard Bernie Sanders speak. "I just fell in love with him," says the chair of the Howard County Democrats, remembering the 2015 speech. "I thought we needed someone to be a champion." Hubka spent the rest of the cycle knocking on doors for Sanders, introducing him at events, and ultimately becoming a caucus chair for him in Iowa in 2016.

Four years later, Sanders is running for President again—but Hubka isn't with him. Instead, she's endorsed South Bend, Ind., Mayor Pete Buttigieg.

"People have asked me, 'are you just giving up on your ideological position to vote for Pete?' No," she says. She supported Sanders last time, she explains, partly because she opposed the Democratic front-runner Hillary Clinton, and partly because of the unique political moment in 2016. This time around, with President Donald Trump presiding over a scandal-plagued White House and an impeachment inquiry raging on Capitol Hill, Hubka's priorities are different. "I think we need some calm in the nation," she says.

Hubka, it turns out, is not alone. E ven before the Senator's heart attack rocked his campaign in early October, a large chunk of his 2016 supporters were already shopping for another candidate. According to the left-leaning think tank Data for Progress's analysis of a YouGov poll, shared exclusively with TIME, only 65% of people who voted for Sanders in 2016 were considering voting for him again in 2020; 81% said they were considering voting for Warren. When asked to pick just one candidate, only about a quarter of the voters who backed Sanders in 2016 said they'd definitely vote for him again; 42% picked Warren.

While conventional political wisdom suggests that the top-tier 2020 Democrats are divided into lanes—with Sanders and Warren drawing more progressive voters, and Biden, Harris and Buttigieg angling for more moderate ones—voters may not see it that way. Many are like Hubka: making their decisions based on a combination of policy, personality, instinct, and a sense of what the nation needs at this moment—rather than pure ideology.

" People aren’t sitting with a laundry list of issues and checking off where the candidates stand on them," says Anna Greenberg, a Democratic pollster. " There’s a lot of things driving vote choice, but it’s not an ideological litmus test. There is some narrow slice of the electorate that do feel that way, but it’s narrow."

Understanding the limits of ideological fidelity can help explain some puzzling patterns of voter loyalty in the crowded Democratic primary. Why is it, for instance, that polls show supporters of Biden, Harris, and Buttigieg all favoring Elizabeth Warren as their second choice—even though Warren is significantly to the left of their first choices? Or why are more Sanders supporters picking Biden as their second choice, even though Warren is a more direct ideological parallel to the Vermont Senator?

That many Sanders 2016 supporters now lean toward Warren isn't particularly surprising. The two Senators have a long friendship and similar political agendas. Warren's events across Iowa last month were full of voters, like Mark Fuller, a 36-year old who works in education at a community college near Iowa City, who said they'd caucused for Sanders last cycle. Supporting Sanders in 2016 " was an anti-Hillary thing; it was an outsider thing," said Fuller, who wore a T-shirt bearing hundreds of tiny images of Warren's face.

But 2016 Sanders supporters are also curious about many candidates—including moderates who seem to have little in common ideologically with the Vermont Senator. According to Data for Progress, 27% of the voters who chose Sanders in 2016 are now considering Kamala Harris and 32% are considering Joe Biden. A surprising 35% are considering South Bend Mayor Pete Buttigieg. According to a Des Moines Register poll released in late September, 12% of 2016 Sanders voters in Iowa plan to caucus for Buttigieg this time around (that poll has a 4-point margin of error).

The Vermont Senator and the South Bend mayor have little in common: Sanders is a 78-year old socialist who's made a name for himself as an uncompromising political pugilist; Buttigieg is a 37-year old gay veteran who once worked at McKinsey and trumpets a message of principled compromise and unity. If Sanders' brand appeals to the lefty idealist, Buttigieg's is designed for the moderate pragmatist. Sanders champions of Medicare for All; Buttigieg offers Medicare for All Who Want It. Sanders proposes free college for all and promises to cancel all student debt; Buttigieg's college affordability plan offers an incremental free college program to low-and-middle income families on a sliding basis. Sanders is a democratic socialist ; Buttigieg calls himself a "democratic capitalist."

And yet, voters don't seem to care about the contradictions. In Iowa, Buttigieg events are full of people who say they caucused for Bernie Sanders in 2016, and his appeal appears to be widespread. A week before Sanders's heart attack, both candidates held campaign events in Dubuque : Sanders drew about 200 people ; Buttigieg drew roughly four times that.

"What I like about Pete is he has the values, but he's not as combative," says Shannon Schott, a 25-year-old nonprofit program director. Both she and her husband Gabe, a 28-year-old band teacher, caucused for Sanders in 2016 but plan to show up for Buttigieg in 2020. Elizabeth Hendrix, 62, who works in customer service, also caucused for Sanders in 2016 and plans to support Buttigieg next year. "Bernie's four years older now—it's time to get some of these old people out of there," she says. "Personality is a huge part of it," she continued. "Bernie seems so angry all the time. Pete is positive and he feels like he's a force for good."

Brenda Masters, a 50-year-old project manager, caucused for Sanders in 2016 but has come to the Iowa Falls event in a golden Buttigieg campaign T-shirt and carrying a massive cutout of the South Bend mayor's face. "Between Bernie and Hillary I caucused for Bernie, but I don't think what he's representing is a realistic path forward," she says. "I don't know where he hides his magic wand and it makes me nervous." When I asked Masters to rank her enthusiasm for Buttigieg on a scale of 1 to 10, she said she was a 5 for Sanders in 2016, but she's a 20 for Buttigieg this year. In other words: "I did not carry around ginormous Bernie heads at any point."

The number of Sanders defectors may be increasing. The YouGov poll, which surveyed nearly 1300 likely primary voters, and had a margin of error of 3.5%, was taken from Sept 23-Oct 4—before the details of the Senator's Oct 1 heart attack were widely known. In the weeks since, Sanders has taken a break from the campaign trail, dipped in the polls in early states, and is heading into Tuesday's primary debate with a need to prove his physical strength as well as his political viability. (The Sanders campaign did not immediately reply to requests for comment.)

It's impossible to measure exactly how Trump's presidency has changed the political calculus for 2016 Sanders voters going into 2020. Polls consistently show that Democrats are prioritizing candidates who they believe can win in a general election against Trump, and many say they are looking for someone who can unify a deeply partisan electorate. For voters like Hubka, temperament and electability are more important than ideology. While she knows she's more progressive than Buttigieg, she says she's willing to sacrifice that ideological purity for a Democrat in the White House. "There's something there that makes me feel like [Buttigieg] is so much more electable, even though my heart of hearts is more left than him," she says. "I want everyone to be where I'm at, but they're not."

She compares Buttiegieg to John F. Kennedy and Barack Obama, and describes him as "someone that this town, which was very divided, could get behind." And that, she says, is enough to win her vote.