Nicole Guerin, 41, takes a break in a Burlington, Vt. cafe on Oct. 18. Guerin plans to write in former Democratic candidate Bernie Sanders over Hillary Clinton in the general election. (David Weigel/The Washington Post)

Nicole Guerin, 41, had “some real trouble with the breakup.” That was her term for the end of the Bernie Sanders campaign.

It was the first political cause she had thrown her body and soul into, and the senator had won the biggest landslide in the history of the Vermont presidential primary. When Sanders endorsed Democratic nominee Hillary Clinton, Guerin could not follow.

One day, after plenty of misery, she walked out of her house and knocked on the door of a neighbor who, like most people in Burlington, had voted for Sanders.

“I asked, ‘Will you write in Bernie?’ ” Guerin remembered over breakfast at a downtown Burlington cafe last week. “And he said, ‘Of course.’ There was that feeling, that optimistic feeling, I’d been missing.”

For weeks, Guerin became part of a loosely organized campaign to win Vermont for Sanders by writing him in. In most years, it would have been unthinkable — canvassing for a write-in campaign without the candidate’s go-ahead. According to the Federal Election Commission, just 136,040 write-in votes were cast and tabulated in the 2012 election.

Evan McMullin, a conservative independent presidential candidate, speaks at a town hall meeting in Logan, Utah, on Oct. 12. (Eli Lucero/AP)

But this year, that number could be much higher, with multiple campaigns underway to normalize the act of writing in a name. During this month’s scramble to back away from GOP presidential nominee Donald Trump, Republican senators including Kelly Ayotte (N.H.) and Rob Portman (Ohio) said they would write in the name of Indiana Gov. Mike Pence (R) for president, tacitly encouraging others to do the same. Evan McMullin, the independent conservative candidate who entered the race too late to appear on many ballots, will be an “official write-in candidate” in most of the country.

That means that in all but eight states, write-in votes — assuming they are spelled correctly and legible to vote-counters — will add to McMullin’s tally. Several fringe candidates have earned similar status, and some of Sanders’s die-hard fans are spreading the word that many states will also count any ballot with his name scrawled across it, instead of Clinton’s.

Although Clinton’s favorability rating has ticked up in recent weeks, many voters are already casting ballots in an environment where both major presidential candidates are unpopular. McMullin — who has fought his way into a tie in Utah, where he is on the ballot — has benefited from that dynamic in write-in states.

“We have volunteers who are evangelizing,” he said in an interview recently in Salt Lake City, pointing out that Mormons who have done missionary work have built enviable door-to-door skills.

In Utah, hundreds of people have volunteered to canvass and call for McMullin. And in the states where he does not have time to campaign, there are McMullin clubs and write-in efforts. Before he goes to sleep, McMullin likes to “peek below the hood” on social media to find new activists on board.

In recent weeks, Google search-traffic data has showed his name surging in Ohio and Arizona, two states where he is a write-in candidate.

According to more data released by Google, searches for “write-in” have spiked ever since The Washington Post’s release of a 2005 hot-mic recording of Trump, in which he boasted about forcing himself onto women. In six of the 10 states where “write-in” search intensity has been the highest, Sanders is the most frequently searched politician.

One problem: Write-in votes are not treated the same as filled-in ballots. In many states, the votes are not counted or reported at all. In others, a misspelling or an alternate name — say, “Evan McMullen,” or “Bernie” instead of “Bernard Sanders” — would not be tallied.

Another, bigger problem: Sanders does not want voters to write in his name. In interviews with The Post and other outlets, he has repeated a mantra: “This is not the year for a protest vote.” Ever since demonstrators at the Democratic National Convention hoisted “Bernie or Bust” signs, Sanders has asked the people who followed him to focus on giving Clinton a progressive, Democratic Senate.

Not every follower listened. Guerin, emboldened by the support she saw for Sanders, expanded her personal campaign and looked for allies. She found a few in Vermont — some in Burlington and some in Brattleboro.

She found more online, on the constellation of progressive websites that published the sort of news thirsty Sanders fans were craving. In September, a Sanders supporter named Dawn Papple told readers of that “if Berniecrats decided to focus all of their energy phone banking, Facebanking, writing letters to the editor, and knocking on doors in a few targeted areas, Sanders could end up winning at least one state, maybe two.”

Not long after, Indiana activist Michael Sparks, 43, published a story with the clickable premise that Sanders could “become president with only 130,000 votes.” All it would take, he wrote, was a guerrilla campaign in Vermont, and a victory there that would deny Clinton and Trump the 270 electoral votes needed to win the presidency. It was exactly what McMullin hoped to see in Utah.

“If we relocate to Vermont for one month (something I am already making arrangements to do) then we would need to knock on 10,000 doors per day,” he wrote. “If each activist knocks on 300 doors per day then we would need 30 dedicated people to relocate to Vermont from early October through November 8.”

Last week, Sparks was making his final preparations to drive himself and a half-dozen Sanders supporters to Vermont. The plan had changed somewhat — for him and Guerin.

“Trump’s collapsing,” Sparks said. “So our mission statement went from ‘Let’s get Bernie into a contest in the House of Representatives’ to Clinton having a lock on the presidency. What I want now, and am trying to sell to people, is: Let’s just honor Bernie Sanders. Make him the president of Vermont.”

It was ambitious: A campaign, organized online but backed by real-world organizing, to get 100,000 Vermont voters to write in Sanders. But it was quickly canceled. In text messages posted by Sparks, Guerin told him that she had broached the topic with Sanders’s wife, Jane. On Twitter, the rumor grew quickly enough that Jane Sanders swatted it down.

“I would never say not to support Bernie or tell ppl how to vote,” the senator’s wife tweeted. “I do think DT is dangerous & needs 2 b beaten.”

By that point, Sparks had already aborted his idea of driving the 14 hours from Indianapolis to Vermont. A full-blown row had broken out among online activists debating what the best protest vote would be — whether writing in Bernie detracted from Green Party candidate Jill Stein, for example.

For Guerin, the end was merciful. “I was hitting a wall,” she admitted, as she finished her coffee. “I kept hearing, ‘This is like Ralph Nader, a wasted vote.’ I kept hearing no, from some of the best Bernie canvassers.”

She did not rule out another round of door-knocking. She texted a friend, to see whether she might be up for it. But it was unlikely.

“I don’t want to put my heart and soul into something again and come out with nothing,” she said.

James Hohmann in Salt Lake City contributed to this report.