Early in last night’s proceedings, several cable news reporters with “sources” inside the Clinton campaign reported an item that was glaringly obvious to anyone who had followed the Democratic race: Clinton wanted to win Mississippi and Michigan by healthy margins, add to her delegate lead, and declare the nomination contest over. This was a night to bury Bernie Sanders.

From a narrative perspective, it wouldn’t have been a huge stretch. The early primary and caucus map favored her candidacy, with the southeast dominating Super Tuesday to an absurd degree. She killed there, dominating the black vote and running up huge margins in places like Texas, Georgia, Alabama, Tennessee, Arkansas, and Virginia. She followed that with a narrow win in Massachusetts, which was a state that Sanders would have been expected to win if he had a real shot at the nomination. Sanders went on to win three of the four states last weekend, but it was a foregone conclusion that Clinton would roll in Mississippi, which left Michigan as the big prize—win there, and Sanders would be reeling. Even if he stayed in the race, she could effectively shift to the general election and behave as though the nomination were a foregone conclusion.

Polls in the week leading-up to last night’s Michigan primary showed her with a 20-point average lead, which is statistically insurmountable—barring a miracle. Of course, as we saw, the miracle happened. Sanders pulled off what FiveThirtyEight called “one of the greatest upsets in modern political history,” and elevated his own status in the process. Michigan, unlike the other states he’s won, has a large population and a significant minority base. The fact of prevailing here redefines what he can accomplish on a national scale, and ensures his continued presence in the race. Along with the benefit an insane war chest from one of the greatest grassroots fundraising operations ever, he now has the attention of the media, which has thus far been content to ignore him in favor of the Donald Trump sideshow. Last night’s win will change how people think about this race, and it guarantees that Sanders will stick around until the convention. The game, unfortunately for Clinton, is afoot.

Sanders is like a dogged veteran boxer fighting a world champion—nobody really thinks he can win, but he refuses to get knocked out, and the deeper this fight goes, the more dangerous it becomes for the champ. And what’s so interesting about the 2016 race, when you consider the philosophical split in the Democratic party, is that Sanders has backed Clinton into a strategic corner.

Consider her options. First, she could step up her attacks on Sanders. The Clintons always campaign negatively, and this race has been no different. Hillary’s camp has leveled every accusation in the book at Sanders, from sexism to racism to their most recent tactic of arguing, very disingenuously, that he opposed the auto bailout. The product of these attacks, along with several other factors—the DNC stacking the deck against Sanders and corporate media bias among those with close ties to Clinton, to name two—has led to a growing movement sometimes referred to as “Bernie or Bust.” Essentially, progressive voters are promising not to vote for Hillary Clinton in a general election because of the perceived corruption surrounding her campaign, along with her ties to Wall Street and corporate America. The negativity is part of this aura—they see their preferred candidate getting screwed, or attacked unfairly, and her support dwindles.

This is the problem with going negative—the longer Clinton has to fight Sanders, and the more she tries to undermine him in ways that are perceived as dishonest, the more support she loses from the left in a general election. And the same is true, frankly, of Independents, who she continues to lose in huge numbers in states with open primaries. Young people, too, are less likely to support a “negative” candidate, particularly having come of age in the Obama political climate, with its pervading sense of optimism. Clinton struggles with these demographics against Sanders already, which is why she so badly wants her opponent to be Republican as soon as possible—there, she can paint ideological and behavioral contrasts that will attract young people and progressives and independents. Against Sanders, those contrasts all work in his favor, which forces her to run a defensive race.

(There’s also the question of whether that negativity even works. Some argue that her support among black voters in the south is a direct result of highlighting Sanders’ divisions with Obama, but the Sanders campaign made the argument last night that her attacks on the auto bailout turned off Michigan voters who saw the lie, and actually helped Sanders pull off his upset. It’s not clear whether either of these talking points is true, but for historical reference, we can go back to 2008, when Clinton’s negative campaigning made a bad situation worse.)

This problem also shows why the “Sanders makes Clinton a better candidate!” talking point is deeply flawed. In fact, what he’s actually doing is exposing her progressive blind spots, of which there are many, and thereby turning many on the left against her. The longer he’s in, the more trouble she encounters. Furthermore, her negativity will only ramp up the similar responses from the Sanders side, with the intent of drawing more and more attention to all the ways in which Clinton may not be an ideal progressive candidate. None of this, it’s fair to say, is beneficial.

But what are the other options? Clinton would be hard-pressed to suddenly start running a positive campaign and treating Sanders like a valued colleague rather than a dangerous opponent. First of all, that’s not her natural disposition. Second, he has real momentum on a national level, as you can see in the graph of polls from the last year, and it seems to be the case that the more people become familiar with him, the more support he gains. It’s a trajectory Clinton remembers from her race against Obama, and it’s not exactly a great idea to sit back and let the process play out—it could end badly for her. The temptation to nip this in the bud and deliver the knock-out punch is strong, but the problem is that each attempt to deliver that punch leaves her vulnerable.

Let’s go back to the boxing analogy for a moment. Hillary, the champ, is winning the fight as we enter the middle rounds, but there aren’t many who expected her opponent to still be on his feet at this point, much less looking dangerous. Now, let’s suppose that instead of getting to rest for six months after the fight, Hillary has another fight a week later. Each blow she takes, and each round she has to last, saps her energy and hurts her chances in that second fight. The solution is obvious—go super-aggressive and send her opponent sprawling to the canvas, ending the fight once and for all. But the problem, in boxing as in politics, is that these sorts of attacks will leave her exposed.

Going on the offensive is a risky maneuver for Clinton, but so is sitting back and passively hoping for the best. There’s no good option here, which is why we’ll likely see a middle ground approach—a few attacks on policy differences, while attempting to restrain the viciousness that could cost her more votes in November with the young and progressive and independent. She still has the advantage, and will likely have to resign herself to “grinding it out” until the convention this summer. The dream of the quick finish died with Michigan, and now she has to play the long game. Meanwhile, she must envy Sanders, who can deliver the same message with the same aggression, and really doesn’t have to deal with the strategic complications besetting his opponent.

Tonight’s Univision debate, which will be simulcast on CNN, should be a good indication of the version of Hillary Clinton we’ll see going forward. But her experience as a nominee, her voting record as a Senator, and her behavior as Secretary of State—particularly in regards to Libya—all give us a strong hint as to which direction she’ll turn. When there’s any uncertainty or doubt, Clinton’s impulse has always been to attack.