The effort now is to make sure things stay that way.
Sanders has vowed to take his campaign to the Democratic convention, but he's also signaled that his effort is now more of a movement than a competitive political machine. He's slashed staff and slowed down his breakneck pace of campaigning.
On the trail, his core issues like income equality and campaign finance reform still loom large, but the senator has taken to reflecting on the arc of his campaign. He frequently reminds his followers that their revolution began as an unlikely campaign that the media and the political class outright dismissed.
"When we began this campaign, nobody really thought it would go very far because many of the pundits were saying who in America supports the idea of a political revolution?" Sanders said at a campaign rally in Morgantown Thursday night. West Virginia and Nebraska vote Tuesday night.
As Hillary Clinton stands on the cusp of clinching her party's nomination and facing off against Donald Trump, even Democrats supporting her say Sanders has permanently changed the political landscape. He's introduced new ideas that have become fixtures in Democratic debates -- like his signature proposal for free college -- and raised expectations of the party's liberal base.
Under pressure from Sanders and his supporters to embrace more progressive positions, Clinton has reversed her position on thorny political issues like the Keystone XL Pipeline and the Trade Pacific Partnership, coming out against both projects during the primary.
And this week, Clinton also appeared to shift left on health care
, saying she would support giving people the option to "buy into Medicare at a certain age."
"I'm also in favor of what's called the public option, so that people can buy into Medicare at a certain age," Clinton said Monday in Virginia.
Those comments brought her closer to Sanders' support for a single-payer health care program, which the senator dubs "Medicare for all."
Former Pennsylvania Gov. Ed Rendell, who endorsed Clinton but has also publicly praised Sanders' role in the Democratic primary, said the senator's campaign has pulled both the party and Clinton in a more liberal direction.
This shift, Rendell predicted, will not be fleeting: "If he moved the needle from 5 to 9, let's say, it won't always be a 9 -- but it won't go back to 5."
Rendell added that Sanders will have the "rare opportunity" to remain a powerful voice during Clinton's general election fight and beyond 2016. "Most defeated politicians, once their campaign is over, lose their ability to continue to impact," he said. "He, I think, has an increasingly positive opportunity to impact -- if he's willing."
With the end of the primary season just one month away, Sanders' campaign is laying down the groundwork to influence the party platform at the convention in July. On Friday, the senator wrote to DNC Chairwoman Debbie Wasserman Schultz, requesting that he be adequately represented on the various convention committees.
And Sanders told CNN's Wolf Blitzer on Friday he plans to still talk about Clinton.
I will continue to run an issue-oriented campaign," Sanders said. "Will I be taking on Donald Trump? Absolutely. Will I be discussing the differences of opinion Secretary Clinton and I have? Yes I will."
Clinton will have to convince some Sanders supporters that she is worth voting for in November. In 2008, there were plenty of hurt feelings between her camp and Barack Obama backers after the primary, but the party quickly came together. The specter of Trump winning should help Democrats unify, but the more passionate Sanders supporters that turn up to his rallies say they'd rather write-in Sanders, vote for a third party candidate or sit out altogether.
"Whether you support Sen. Sanders or you support me, there's much more that unites us than divides us," Clinton said at a rally last week after winning four of five Democratic contests.
Trailing Clinton by some 300 pledged delegates, Sanders has brought his rallying cry to West Virginia, which holds its Democratic primary Tuesday.
Benjamin Male, a 23-year-old Sanders supporter from Clarksburg, is one of the thousands of young voters who have rallied around Sanders' populist rhetoric. A night auditor at a Marriott who is training to be a manager, Male said he doesn't believe the Democratic contest is over yet and doesn't plan to vote for Clinton in the general election -- unless she were to name Sanders as her running mate.
"He is now the face of this movement," Male said. "So even if he were to drop out tomorrow, this movement is not over."
Alex Mayers, a 29-year-old from Fairmont who is half Costa Rican, said free college is "the single most important" issue currently facing the country. "You can't have a strong country without an educated work force," he said.
Wearing a black T-shirt with an illustration of Sanders smoking a marijuana joint on top of a tank that is pointed at Clinton, Trump, Jeb Bush and Ben Carson, Mayers said he would not vote for Clinton in November and write in Sanders, instead.
For Regina McGraw, a 60-year-old Democrat from Morgantown, her support for Sanders also has much to do with her outright rejection of Clinton. Attending the rally with her son, daughter-in-law and grandchild, McGraw described Clinton as "phony" who has "no idea what it's like to be middle class."
"I think Bernie probably knows the price of milk and I'll bet she has no clue," McGraw said.
When Clinton officially wins her party's nomination, it will have been after a hard-fought battle against Sanders that exposed vulnerabilities of both her candidacy and her platform.
Sanders stormed the national stage at a time when Clinton was struggling and progressive activists were relentless but unsuccessful in their attempts to draft Massachusetts Sen. Elizabeth Warren into the presidential race. He launched his campaign in Burlington, Vermont, last May, telling the crowd that he was sick and tired of seeing a country run by "a handful of billionaires, their super PACs and their lobbyists."
In the months to come, his rallies swelled in size and Sanders soon emerged Clinton's only serious rival.
Day in and day out, Sanders railed against a "rigged economy" and corrupt Washington that he said was doing little to help a declining middle class. The political process, he said, had become a game to be manipulated by the country's elite: millionaire and billionaire donors; powerful lobbyists and special interest groups; and the behemoth financial institutions whose greed, Sanders said, led to the recent economic collapse. The contrast to Clinton was obvious -- she and former President Bill Clinton are prolific fundraisers from big donors and she has collected millions of dollars from speeches to Wall Street.
Sanders has shown remarkable popularity with young voters. He's overwhelmingly outperformed Clinton among voters 18-29 years in age, in some states with more than 80% of support.
Former West Virginia Democratic Party Chairman Nick Casey said he has not seen the current level of enthusiasm among young people in decades. "I'm a child of the '60s and it reminds me of the days when there was some motivation and interest driven by a very bad reason, the Vietnam War, when people were excited and interested in what the heck was going on," Casey said. "I think it's great."
Although Sanders was adamant at first that he would not directly go after Clinton, in recent months, that stance has shifted.
He questioned the former secretary of state's paid speeches to banks like Goldman Sachs, calling on her to release transcripts from those events. Sanders also said he questioned Clinton's judgment, pointing to her past support for the Iraq War and international trade agreements, as well as her refusal to denounce a pro-Clinton super PAC.
Anna Greenberg, a Democratic pollster and senior vice president at Greenberg Quinlan Rosner Research, said Sanders' biggest impact on the 2016 race has been to force Clinton to address issues that are top priority for the progressive left.
"There's no question that he raised a set of issues that Hillary Clinton is not terribly comfortable with and more in the wheelhouse of an Elizabeth Warren or a Bill de Blasio -- around inequality, corruption in politics," Greenberg said.
The criticism that Clinton has fielded from Sanders, Greenberg added, will ultimately work to Clinton's benefit as she gears up to take on Republican presumptive nominee Donald Trump in November. Like Sanders, Trump has touted a populist message, denouncing outside money in politics and promising to fight for the disenfranchised.
Clinton "has no choice but to continue with it," Greenberg said, "if for no other reason than Trump is very effectively running as an outsider for the little guy, anti-politician, anti-big money."