He lives to fight another day, but pulling off a win will still be tough. Photo: Pedro Portal/El Nuevo Herald/TNS via Getty Images

The March 8 primaries were widely expected to be a predictable blip between the big races on Super Tuesday and March 15, particularly on the Democratic side. But in what FiveThirtyEight’s Nate Silver is calling one of “the greatest polling errors in primary history,” Bernie Sanders overcame a disadvantage of more than 20 points in recent polls to narrowly beat Hillary Clinton in Michigan.

In the famous New Hampshire upset in '08, Clinton trailed Obama by 8 points. Big upset. But today, Sanders trailed Clinton by *21* and won. — Nate Silver (@NateSilver538) March 9, 2016

Many had begun writing off Sanders after Clinton’s big wins in the past two weeks, and the Michigan victory provides the Sanders campaign with a huge momentum boost. Now pundits are questioning polls that suggest Clinton will win easily in Ohio and Illinois next week. FiveThirtyEight’s Harry Enten writes:

The question I am asking myself now is whether this means the polls are off in other Midwest states that are holding open primaries. I’m talking specifically about Illinois and Ohio, both of which vote next Tuesday. The FiveThirtyEight polling average in Illinois gives Clinton a 37 percentage point lead, while the average in Ohio gives her a 20 percentage point lead. If Michigan was just a fluke (which is possible), then tonight will be forgotten soon enough. If, however, pollsters are missing something more fundamental about the electorate, then the Ohio and Illinois primaries could be a lot closer than expected.

Clinton’s still ahead in the delegate count, and it still seems likely that she’ll ultimately win the nomination. However, while Clinton signaled in the past few days that she’s ready to wrap up the primary race and focus on Donald Trump, now it looks like her primary slog with Sanders will continue.

On Twitter, Slate’s Jamelle Bouie argued that’s something all Democrats should be celebrating:

It means more media attention for what is a largely civil and responsible race for the Dem nomination. — Jamelle Bouie (@jbouie) March 9, 2016

Might even juice up turnout a bit, again, a chance to reach supporters. And it's not *that* divisive. — Jamelle Bouie (@jbouie) March 9, 2016

Writing in The Wall Street Journal, Jim Manley, a former aide to Senators Harry Reid and Ted Kennedy, said it’s “pretty clear now that [Sanders] is in this race all the way to the convention in July.” Michigan suggests that Clinton’s hold over black voters isn’t as absolute as previously thought:

But I’d say the fact that Mr. Sanders did so well among African American voters is the most striking takeaway. A lot has been said about how Mr. Sanders is an older white man from a heavily white Northeast state. African Americans have largely been expected to favor Mrs. Clinton and helped deliver her strong win in Mississippi on Tuesday and in other states earlier. In Michigan, Mr. Sanders won his largest share of African Americans in the states contested so far, and the numbers suggest that he is able to do well in more states than many had imagined (myself included).

Slate’s Jim Newell agreed that Michigan shows Sanders is making progress in expanding his coalition — though he notes he only won by two points.

Winning the big prize on Tuesday night helps Sanders mostly in terms of horserace narrative purposes: showing the world that he’s not dead yet … Modest victories, no matter the size of the state, are not going to cut it for Sanders. He needs big victories in big states to cut hard into the pledged delegate lead that Clinton has accumulated. Even if he is able to pull off another squeaker in Ohio next week, Clinton is set to swamp him in the demographically and culturally different — and larger — state of Florida. Winning 30 percent of black voters in Michigan is a move in the right direction, but Sanders needs to start winning majorities of all demographic groups in places like California, New York, and Pennsylvania — all while continuing to win the smaller contests in places like Kansas and Oklahoma that he’s had success with.

But Sanders found a new line of attack against Clinton: trade deals. As the Washington Post’s Chris Cillizza explains:

Almost six in 10 Michigan Democratic primary voters said international trade takes away U.S. jobs, according to exit polling. Among that group Sanders won by roughly 20 percentage points over Clinton. That could — and should — bode well for his efforts in Ohio, Illinois, Wisconsin and other states where international trade has ravaged the economy. “What tonight means is that the Bernie Sanders campaign … is strong in every part of the country,” Sanders said in brief remarks in Florida Tuesday night. “We believe our strongest areas are yet to happen.”

That issue could be a problem for Clinton even beyond the Democratic primary. The Guardian’s Lucia Graves writes:

Clinton thought she had finessed the trade issue, by focusing on other problems in Michigan, like Flint’s lead-poisoned water and by skewering Sanders over his vote against the auto bailout (his campaign said it was part of a bigger vote against a bailout for Wall Street). But clearly she hadn’t. And that’s a troubling finding for anyone worried about a Trump presidency: it suggests the Democrats’ likely nominee could have a problem in crucial manufacturing states.

The Post’s Stephen Stromberg says the issue could even hound Clinton if she manages to win the White House:

Sanders appears to be benefiting from the elements of Trump-like populism that play among some Democrats and independents voting in Democratic primaries, including mistrust of foreigners stealing American jobs. That dynamic should worry Clinton for two reasons. First, Donald Trump and Ted Cruz, the two most likely GOP presidential nominees, both oppose the TPP. Trump has attacked trade deals from the start of his campaign. Cruz is on slightly shakier ground because he had to flip-flop in order to vote against giving President Obama “fast track” trade authority. But he still found his way to voting “no.” In a matchup against Clinton, either of them could make a play for Sanders populists. This may well not be enough to offset the advantage she would have among minority voters, but it is a danger. Second, if Clinton does win the presidency, protectionist sentiment may constrain her from pursuing an assertive international agenda. The following might be terrible political advice — but it would be nice if she would make the argument for broader economic engagement rather than shying from it and still losing.

But for now, Clinton needs to refocus on the race she thought she’d already essentially won.