Even for an insurgent campaign, Bernie Sanders’s presidential candidacy has followed an unusual arc.

Long before he entered the race, the Vermont senator framed the prospect of a White House run as an exercise in giving voice to the progressive left within Democratic politics rather than an earnest effort to win the Democratic nomination.

As far back as 2013, he was telling reporters, “Anyone who really, really wants to be president is slightly crazy,” but that, in the words of the Burlington Free Press, he would run “if no one else with progressive views similar to his ends up taking the plunge.”

The instrumental premise of his campaign shaped a great deal of the early coverage of it, as did Hillary Clinton’s initial dominance. But almost all of the thinking behind that analysis has proven wrong over time. Whether he ever intended it or not, Sanders has become a viable candidate. He may soon become a poll leader outright. The media has largely taken stock of the new reality and adjusted their coverage accordingly. The question, to be answered Sunday when the three remaining Democratic candidates meet for their final pre-Iowa debate, is whether Sanders will adjust as well.

When his poll numbers first started ticking upwards in the spring of last year, many reporters were tempted by the narrative of a Sanders surge, but those temptations were often tempered by a sense that Clinton’s lead was impossibly large, and that Sanders would simply use his growing popularity among young Democratic voters to push her leftward, before exiting the race.

By the end of the summer it was clear that Sanders had reached striking distance, and it had thus become impossible to treat his campaign as a largely symbolic affair. Yet, no sooner had this air of seriousness overtaken his candidacy than Clinton seemed to reassert her dominance. In October, she won the first Democratic debate, she (probably) intimidated Vice President Joe Biden out of entering the race against his own wishes, and she humiliated the snarling Republican members of the House Select Committee on Benghazi over twelve hours of testimony. As her lead widened, Sanders seemed to accept her inevitability. He treated her with unexpected deference in debates, and stayed conspicuously quiet about her in general, until an explosive altercation with the DNC over his campaign’s access to the committee’s voter files lent his campaign new vivaciousness. His re-energized outfit is now either gaining on Clinton, or expanding his lead, in national and early-state primary polls.

If Sanders’s surge continues apace, he will win in Iowa, win in New Hampshire, and quickly be vying for 50 percent of the national Democratic vote.

Conventional wisdom continues to suggest that Iowa and New Hampshire, where the Democratic electorates are unusually white, combine to create a false impression of Sanders’s strength—that he will falter once he and Clinton begin competing in the more ethnically diverse states of the South and interior West. If the past year proves anything, though, it’s that skepticism of the conventional wisdom is urgently in order.

Even Clinton seems to be questioning it. Her campaign’s oddly framed attacks on Sanders’s single payer advocacy connote an urgent desire to blunt his momentum. And yet, Sanders himself still seems shaped by the idea that he was never supposed to get this far. His ads, the way he parries with Clinton in general, convey an ambivalence about his own strength that make it hard to imagine him pressing his advantages and making Clinton work for delegates she’s probably taking for granted.

Sanders, as New York Times columnist Ross Douthat has noted, often renders his criticisms of Clinton in the most positive possible light, prefacing his answers to debate questions with compliments and qualifiers. His rejection of her fondness for regime change comes only after he offers up praise. “The secretary is right,” he says. “This is a terribly complicated issue.”

If he were to quite literally turn that formulation on its head, it would signal that he’d resolved his ambivalence in favor of taking a real run at the nomination.

As a first-time candidate for president, Barack Obama often attacked his rivals allusively, but he was also unafraid to render any of his attacks in stinging fashion. Around this same time in 2008, at a sanctioned debate in Los Angeles, Obama didn’t backload his disagreements. He accused Clinton, rather disingenuously, of wanting to “force people who don’t have health insurance to buy it,” and suggested she lacked “the kind of judgment that will ensure that we are using our military power wisely.”

This, of course, infuriated Clinton supporters, some of whom threatened to sit out the general election or even support John McCain. But the moral of the story is that Obama won the primary and managed to reunite the party without much hassle. The difference is that unlike Sanders, nobody ever doubted that Obama really wanted it.