When he was in college, Charles Frantz didn’t care about politics. I know because I was friends with him then. He was more a fan of standup comedy, David Lynch films and electronic music. But over the past 12 months, his Facebook feed has become a steady stream of Bernie Sanders news and photos from rallies supporting the senator from Vermont. Charles, now 27, works as a software engineer in New York. He started volunteering with Bushwick Berners — a group of Sanders supporters in Brooklyn — and has donated $2,700 to the Sanders campaign, the maximum allowed.

The election “has permanently made me more politically engaged — it’s changed my life in that way,” he told me. “I’ve started to pay attention to the news a lot more. We’ll see what happens once the presidential election season is over.”

The Sanders campaign has had a galvanizing effect for many people, on social media and in real life. On Monday night, the Associated Press reported that Hillary Clinton had secured the Democratic nomination, according to its survey of superdelegates. The Sanders campaign said it’s not over yet. At a news conference in San Francisco earlier in the day on Monday, on the eve of the California primary, Mr. Sanders noted that his campaign has drawn the support of voters under the age of 45 “in overwhelming numbers.” But his supporters can do their own delegate math and understand the realities of the end of the road. The question they’re left with is: What now? In their own words, here is where Mr. Sanders’s legion of supporters plan to take the “political revolution” next.

In conversations I had with more than a dozen Sanders supporters, many of them told me they were either disillusioned with or apathetic toward politics before this campaign. Mr. Sanders, a 74-year-old democratic socialist from Vermont, energized them unlike any candidate before. Now, depending on how the Democratic primary turns out, they’ll either resign themselves to voting for Hillary Clinton, redirect their efforts to local campaigns or drop out again.

While a few die-hard Sanders supporters have vowed that it’s “Bernie or bust,” a Quinnipiac University poll from late May found that three-quarters of Sanders supporters would vote for Mrs. Clinton if it came down to a Donald Trump-Hillary Clinton race in November. Alex Sheehan, 29, an digital media entrepreneur in New York, said he thought that when faced with the prospect of a Trump presidency, most Sanders supporters would end up voting for Mrs. Clinton — and “If not, we deserve the catastrophic failure that follows,” he said.

“I’ve said it in jest that if it’s Hillary versus Trump, I will go into the voting booth and Snapchat myself voting for Trump for performance art. But I wouldn’t really do that,” he said. He paused. “Maybe I am a Bernie bro!”

This month, after the primaries are all over, some Sanders supporters will try to answer the question of what’s next at an event called the People’s Summit in Chicago. The mission of this gathering: to figure out how to turn Mr. Sanders’s momentum into lasting change. One of the attendees will be a digital strategist named Winnie Wong. After working with the Occupy Wall Street movement, she helped start the grass-roots group People for Bernie, and has been credited with coining the hashtag #FeelTheBern. She said she saw a connection between the Occupy movement and the Sanders campaign.

“This is a movement,” she said. “It is not about Bernie Sanders. He’s a part of this movement.” And, according to Mr. Sanders’s most ardent supporters, that movement isn’t going anywhere.

Tyson Manker was an infantry Marine during the invasion of Iraq. When he was 21, he says, he hung out with a few fellow Marines off base and smoked marijuana, for which he was given an “other than honorable discharge.” That meant he lost aid he would have received under the G.I. Bill.

“I was suicidal and using drugs and alcohol hard core for the first years after they booted me out,” Mr. Manker said. “It infuriates me. It tells me there’s something wrong with the system.”

Last June, he drove the five hours from his hometown, Jacksonville, Ill., to Des Moines to attend one of Mr. Sanders’s first campaign events. After learning about Mr. Sanders’s record on veterans issues, Mr. Manker helped create the group Veterans for Bernie.

Now, he is running for county state’s attorney. He wants to fight public corruption and install a separate court system for veterans.

“Win, lose or draw, there’s still all these millions of people like myself who are going to be far more involved,” he said.

Molly Grover, 30, is one of those people. She lives in Ithaca, N.Y., where she works part time as a nanny. She volunteers 20 to 30 hours a week for a People for Bernie affiliate, Women for Bernie.

Ms. Grover grew up in Vermont, where she thought of Mr. Sanders as a “grandfather figure.” Like many of the people I spoke with, she didn’t consider herself politically active before she signed on to the Sanders campaign. Now, she says she can see herself running for local office someday.

She said she had been able to meet dozens of like-minded progressive women through her work for the campaign, and felt grateful that it had brought a “political sisterhood” into her life.

Anoa Changa, 35, is a lawyer in Atlanta who oversaw grassroots social media efforts in support of the Sanders campaign in Georgia. She recently started volunteering for a new group called Brand New Congress, which hopes to channel Sanders supporters’ enthusiasm to elect progressive candidates to Congress. The group was started by two Sanders campaign staff members who were among the hundreds laid off this spring. This month, Brand New Congress started a 100-city “barnstorming” tour — similar to what Mr. Sanders did at the outset of his campaign — to push for a more progressive Congress.

“It’s getting people to understand that this is more than just casting your ballot every four years or every two years,” Ms. Changa said. “It’s not about the presidential election. It’s whether we’re participating in mayoral elections, city councils, statehouses.”