“Forget it,” Bernie Sanders grumbled. “I don’t want to get into process questions!”

It was an afternoon earlier this winter, and I had come to the Vermont senator’s office in Washington to ask him a version of the question that has consumed the Democratic Party, and liberal politics in general, for close to three years now: What does Bernie want?

Back in the summer of 2016, after Sanders’s long-shot presidential campaign had come shockingly close to clinching the Democratic nomination, the question was: What did he want in exchange for dropping out of the race and backing Hillary Clinton? Then, when Donald Trump was elected, the question was: What did Sanders—who’d spent a quarter century in Congress as the quintessential, minimally effective gadfly—want to do with his newfound prominence?

Today, the question has taken its most urgent and consequential form to date: What does Sanders, with his sky-high name recognition and legions of supporters, want to do in the 2020 presidential race?

Suffice it to say, it’s a question Sanders has been pondering ever since Trump won—not just with friends and family and advisers but over and over in his own head. It’s not, however, a question he likes to kick around with reporters. And now, shifting in a chair at the head of a long conference table, he seemed as tightly coiled as the mousetrap that sat on the floor in the corner of the room. (The dirty secret about Capitol Hill is that it’s infested not with lobbyists but with rodents.) I asked whether he was ready for the vicious attacks he’d face in another presidential campaign? “I know you’re well-intentioned, but it’s political gossip!” he replied. Did it give him any pause that a number of Democratic presidential candidates looked like they were trying to steal his platform? “You’re into gossip!” he said.

In some respects, Sanders was the same irascible, iconoclastic figure that afternoon that he’s always been. His nimbus of white hair was typically unkempt; the dandruff on the shoulders of his blue suit was as plentiful as ever. He was as averse to schmoozing as he was when he arrived in the Senate in 2007. In one of his first days on the job, Sanders bumped into then New Mexico senator Pete Domenici in one of the tunnels underneath the Capitol. The two said hello and had what Sanders thought was a perfectly pleasant exchange—until shortly thereafter, when Sanders received a personal note from Domenici profusely apologizing for their curt interaction. “He hates the word, but there’s an authenticity to Bernie,” says Faiz Shakir, a former Sanders adviser. “The curmudgeonliness is the same on and off the screen.”

But in other, more profound ways, Sanders has become an entirely different person. In the nearly four years since he announced his first presidential campaign, he has done more to remake the modern Democratic Party in his image than any politician since Bill Clinton—and that includes Barack Obama, who not only spent eight years in the White House but also was a Democrat. (As his friends and foes often emphasize, the socialist Sanders does not serve in the Senate as a Democrat but rather as an independent who caucuses with the Democrats.) Medicare for All, a $15-an-hour minimum wage, free college—the issues that he championed during the 2016 Democratic primary and that Hillary Clinton dismissed as naive and unrealistic—are now mainstream Democratic Party positions. “We are where we are,” says Shakir, who’s now the ACLU’s national political director, “because Bernie forced the party to rethink everything.”

“The enormous capability of a president to bring change is something that is kind of awesome, and that is enticing,” Sanders said when I asked what he finds appealing about becoming president.

Having toiled his entire political career as a gadfly, Sanders is now a prophet. “The ideas we brought forth in 2016, which were considered, not only by the Democratic establishment but by the editorial writers, to be extreme and fringe and out of step with where the American people are,” Sanders told me, “are now what is in, by and large, the Democratic national platform and are being adopted by candidates across the country.” What’s more, the Democratic Party’s future—as reflected by the remarkable rise of the 29-year-old New York congresswoman Alexandria Ocasio-Cortez—has clearly tilted to the left. This development has been as satisfying for Sanders as it was unexpected. “We have had more success in ideologically changing the party than I would have dreamed possible,” he said. “The world has changed.”