Over the past few weeks, Sen. Bernie Sanders’ (I-VT) presidential rivals have settled on a familiar line of attack against him: For all his talk of revolution, Bernie—they say—got painfully little done while in office.

“This crisis demands more than a senator who has good ideas,” said Sen. Elizabeth Warren (D-MA), in what was her sharpest rebuke of her ideological co-traveler to date, “but whose 30-year track record shows he consistently calls for things he fails to get done and consistently opposes things he nevertheless fails to stop.”

That line, like similar ones offered by former Vice President Joe Biden, was meant to undercut the notion that Sanders can deliver the big changes he’s promising. And, for the purposes of those making the accusation, it has the virtue of being statistically true. Of the 422 bills for which Sanders has been the lead sponsor during his nearly 30 years in Congress, only three have become law, according to Congress.gov. Two of them were perfunctory bills to name post offices.

“Sen. Sanders is not a team player,” one former lawmaker told The Daily Beast. “He is an ideologue, he is rigid, he is inflexible—he has a point of view that is locked down, and it’s not going to change; he’s not interested in compromise.” The Senate, said a former colleague of Sanders’, “is a place where almost everything is done with others. If you’re going to be effective and get things done, you have to work with others. That’s not Sen. Sanders’ typical style.”

Presented with these rebukes, Sanders has often bristled. During an appearance on 60 Minutes, he noted that he had passed more “bipartisan amendments” than anyone during his time in the House, and he pointed as well to his signature contribution to the Affordable Care Act—a provision providing for $11 billion in funding for community health centers. Effectiveness can be measured in a number of ways, Sanders told host Anderson Cooper: “Congress is a complicated place.”

Congress is, indeed, complicated. And so is Sanders’ legacy inside it.

On the surface, he appears to be just what Warren alleged: a man who served decades in office with little to show for it.

“ He has really accomplished very little legislatively. He has accomplished a lot in terms of ideology. And that’s an important role. ” — former Rep. Barney Frank

But even some of his detractors concede that his impact cannot simply be measured in the number of bills passed. Whereas the vast majority of lawmakers have chosen to play the inside game—crafting compromises, extracting concessions, and leaning on leadership—to score legislative victories, Sanders, in the back end of his career, discovered that he could leverage power from the outside, using public spectacle, media ubiquity, and grassroots pressure campaigns to move the legislative debates in ways that he never was able to earlier in his career.

“He has really accomplished very little legislatively,” said former Rep. Barney Frank (D-MA), a consistent Sanders skeptic. “He has accomplished a lot in terms of ideology. And that’s an important role, to be the guy out there speaking.”

From conversations with over a dozen of Sanders’ current and former colleagues, former senior Democratic aides, and others who have closely followed him over time, what emerges is a picture of a lawmaker who can plausibly claim credit for major victories on Capitol Hill but who operates in a way that sets him totally apart: uncompromising, powered less by his relationships in the Capitol and more by his base of outside supporters, and, at the end of the day, focused on moving the conversation as much as moving legislation.

“People inside the Beltway, often, we think alike—we do the same shit over and over,” Rep. Mark Pocan (D-WI), a Sanders supporter, told The Daily Beast. “We don’t necessarily get a whole lot done, especially in the last decade or so. And I think, you know, the idea of building a movement of grassroots support for an issue, so that you can then influence legislators based on their constituents, is to me the smarter approach.”

“He hasn’t had anything done,” Pocan added sarcastically, “which is why every candidate now is talking about Medicare for All or universal health care.”

It wasn’t always this way. Early in his career, Sanders was widely regarded as an odd-duck backbencher who stood out as the lone self-identifying democratic socialist on Capitol Hill. For much of his career, the Vermonter was a peripheral player in Congress’ debates and power dynamics—particularly in the House, where he served from 1991 to 2007. His favored legislative tool was one that legislative rabble-rousers have often leaned on in the absence of better options: the amendment.

Sanders was so prolific at filing amendments that he was dubbed by some colleagues the “amendment king.” Often he’d find someone across the party aisles—usually fellow outsiders like former Rep. Ron Paul (R-TX)—to try to get those amendments passed. He found success, passing more amendments through roll-call votes in a Republican Congress than any other member. But as a 2005 Rolling Stone story detailed, Sanders’ often failed too. Many of his hard-won legislative achievements were usually stripped from the final versions of bills by party leaders who didn’t want to see his proposals become law. Between his years in the House and the Senate, Sanders filed over 500 amendments, with roughly one in five of them getting approved in a vote. Though not all of those were ultimately included on bills that became law, some important ones did: In 2001, Sanders got an amendment on a spending bill that prohibited goods made with child labor abroad from being imported to the U.S.

Some look back at Sanders’ “amendment king” mantle and see it as a sign of his ineffectiveness, not some mastery of the minutiae of the legislative process.

“The reality is, most of his time was spent offering amendments destined to go nowhere because he refused to try to craft compromises with Republicans, much less his Democratic colleagues,” said Jim Manley, a former senior aide to Sen. Harry Reid (D-NV), the former Senate Democratic leader. “He marched to the beat of his own drummer. I don’t believe he felt he was there to cut deals.”

The Sanders campaign did not respond to a request for comment. But while Sanders developed a reputation for not being particularly interested in collaboration, he was never viewed as a nihilist either. When big votes came up, he was ultimately fine not letting ideological rigidity upend incremental reform.

A key instance of this was on Sanders’ signature issue: health care. When Barack Obama took office and Democrats swept the House and Senate, Sanders agitated for the party to push for a so-called public option for health insurance. After Republican Scott Brown’s Senate victory in Massachusetts, the likelihood of passing such a measure vanished. But Obama administration officials said they never feared that Sanders would derail the bill if it lacked the provision. Instead, they asked the senator what he wanted in its place, and he ultimately got on board after securing $11 billion in funding for community health clinics, which often help serve rural or under-covered areas.

“The community health centers that were dramatically increased in funding he can take significant credit for,” said a former colleague. “If a person is being fair about his accomplishments, he can take deserved credit.”

It was late in 2010 that Sanders decided to try a different approach.

The expiration of a number of tax breaks had prompted Obama to deputize Biden to cut some sort of deal with then-Senate Minority Leader Mitch McConnell (R-KY). The resulting compromise—which extended some of the stimulative policies Obama had pushed but also the infamous Bush tax cuts that Democrats had long decried—was presented as a take-it-or-leave-it proposition to the party. Sanders was, by all accounts, repulsed.

But instead of demanding some sort of legislative extraction for his vote, or simply voting against the measure, he chose to hightail it to the Senate floor and launch a de facto filibuster. The resulting eight-and-a-half hour speech was remarkable, not only for its length but for the popular attention it attracted.

“By and large, it is not a good deal. We can do better,” Sanders said. “And if the American people stand up and work with us, if they get on the phones—if they call up their senators, if they call up their congressmen—if they make their voices heard and said, ‘Enough is enough. The rich have got it all right now.’”

“ Bernie’s strength is his authenticity as an outsider—he’s said we were a corrupt oligarchy even before it was true—but as a result, he does not have an impressive record of accomplishments. It’s kind of hard to be both an authentic outsider and an effective insider. ” — former Rep. Brad Miller

Liberals were galvanized and, at Sanders’ urging, began flooding the phone lines of Democratic Senate offices demanding they reject the deal.

The White House began to notice too. As Sanders spoke, Obama went to the briefing room along with former President Bill Clinton, who—clearly delighted at being back in the spotlight—began spinning the deal to the press corps as “the best bipartisan agreement we can reach to help the largest number of Americans.”

Sanders knew he couldn’t stop the vote from passing. Indeed, unbeknownst to his supporters, he’d privately told Reid, then the majority leader, that he wouldn’t torpedo the compromise. But the episode gave both him and his team their first taste of the power they could yield through playing an outsider’s game.

Millions of people who had only a passing familiarity with Sanders—as an outspoken liberal who opposed wars, demanded health care be a universal right, and had made some oddly favorable declarations about communist governments—suddenly were interested in the senator. Sanders turned his speech into a book, which in turn became a bestseller. But, more importantly, his team discovered that there was a growing appetite on the left for progressives willing to call out their own leadership.

Soon, Sanders was making more appearances on television and began forcefully pushing the administration on a variety of fronts. At a fiery speech at the United Steelworkers Convention in 2011, he implicitly blasted Obama for considering Social Security benefit reductions as part of a fiscal deal with House Republicans.

That same year, he floated the idea that it would be good to have the president primaried from the left—a seemingly quixotic proposal at the time but a pronouncement that caught the administration’s attention.

“I don't recall ever really having to think about him during those early year debates. It was just, ‘Oh, it's Bernie,’” said one former top Obama official. “And then, suddenly, you had to start thinking about him.”

Sanders denied he ever personally considered launching a primary bid and he never did. But he continued to build on his outsider approach in the years that followed Obama’s re-election. In 2013, he spoke at a rally outside the White House to denounce proposals for entitlement reforms, once again implicitly criticizing Obama. In 2015, as much of the Democratic Party was rallying around a proposal to raise the minimum wage to $10.10 an hour, Sanders decided to go far further, introducing a bill to raise it to $15 an hour. In the years that followed, he heightened his demands for Medicare for All, even as much of the Democratic Party remained focused on staving off efforts to kill or roll back Obamacare.

Sanders’ increasingly public style grated some of his colleagues, who watched as their efforts to craft some semblance of legislative compromise (including securing some Republican co-sponsorship for a minimum wage hike) would inevitably become portrayed as morally insufficient by a senator with little history of legislative results.

“ I don't recall ever really having to think about him during those early year debates. It was just, ‘Oh, it's Bernie.’ And then, suddenly, you had to start thinking about him. ” — former top Obama official

“Bernie’s strength is his authenticity as an outsider—he’s said we were a corrupt oligarchy even before it was true—but as a result, he does not have an impressive record of accomplishments,” said former Rep. Brad Miller (D-NC), a progressive minded member who has endorsed Warren. “It’s kind of hard to be both an authentic outsider and an effective insider.”

But others argued that the Sanders approach yielded demonstrable results. By summer 2019, all but a handful of the members of the Democrats’ new House majority had voted for legislation to raise the minimum wage to $15, and none other than Amazon—Sanders’ corporate bête noire—had decided to raise wages to that level for a good chunk of its employees. Support for Medicare for All had grown among Democrats as well: 119 House Democrats and 14 Senate Democrats are now co-sponsors of legislation to establish such a health care system.

Former Rep. Keith Ellison (D-MN), who has been a vocal supporter of Sanders’ two presidential campaigns, pointed to that minimum wage push as an example of the senator’s political prowess. When he was in the House, Ellison, now attorney general of Minnesota, was the lead sponsor of legislation to raise the wage to $15 an hour. Sanders was his counterpart in the Senate. Ellison told The Daily Beast that they didn’t make just symbolic progress together—they laid the groundwork for major change for whenever Democrats increase their power in Washington.

“By the time I left, we had the majority leader, we had Nancy Pelosi, we had the committee chairs” behind the bill, he said. “If we get some Democratic senators, that’s gonna be the law. And Bernie was the one pushing it… Congress does have the dynamic of the workhorse and the show horse. I’m not going to name the show horses, but Bernie was definitely in the workhorse category.”

Whether this makes Sanders an effective politician or not depends, in large part, on one’s definition of effectiveness. The senator doesn’t have a signature piece of legislation. But not many lawmakers play that type of role.

“If you spend some time around here,” said Sen. Dick Durbin (D-IL), the No. 2 Senate Democrat, “you’ll notice that criticism could be leveled at a lot of people.”

And contrary to Sanders’ reputation as politically stubborn and morally self-righteous, there have been instances where he has compromised on his own ideology. In 2014, he and the late Sen. John McCain (R-AZ) reached a compromise to address crisis-level wait times at Veterans Affairs hospitals that was philosophically at odds with Sanders’ world vision. The bill they agreed to included half a billion dollars in new funding for VA facilities and construction but also made it easier to fire VA officials and allowed veterans to use private health care facilities outside the government system if their local VA facilities were overwhelmed.

“I would have written a very, very different bill,” Sanders said when the deal was reached. “Right now we have a crisis on our hands, and it’s imperative that we will deal with that crisis.”

But the VA deal is rarely, if ever, brought up as a signature Sanders moment, in large part because it stood out for how little it resembled the type of legislative style he likes to deploy. Instead, for Democrats, it is another bill that is often described as quintessential Bernie.

In January 2017, Sanders pushed an amendment, alongside fellow 2020 contender Sen. Amy Klobuchar (D-MN), to allow Americans to buy cheaper prescription drugs imported from Canada. While it was supported by most of the Democratic caucus, it proved to be a tough vote for some, like Sen. Cory Booker (D-NJ), who represents a state with a significant drug industry presence.

Their amendment narrowly failed, with 13 Democrats joining most Republicans in voting against it—including Booker, who took heat for his vote.

“He forced a vote on an issue he knew roughly a dozen Democrats were gonna vote against him on,” said a former Senate aide, referring to Sanders. “He’d rather do that, make a point, and hold Democrats’ feet to the fire from the left than not doing that and building better relationships that could get something passed.”

That Sanders pushed the amendment after his surprisingly successful primary run in 2016 is no accident, said the former Senate aide. “I think he felt he could throw his weight around a bit more, and he chose to do it in a way that pulls the party to the left as opposed to using his increased clout to make constructive policy.”