Bernie Sanders’s political coalition – a mix of young, liberal, and independent voters – reasserted itself last night, boosting the Vermont senator to an unexpected win in Michigan, contradicting polls that had predicted a double-digit loss.

Sanders made up part of that ground by winning over voters who said they decided within a week of casting ballots, according to CBS exit polls. But his lead among that group – 7 percentage points – is not enough to explain the gulf in support Sanders was able to close.

His victory was likely fueled by strong turnout among voters with whom Sanders performs best. According to the Detroit Free Press, more than 2.2 million voters turned out to cast ballots in the Democratic primary.

Sanders won his typically huge share of voters ages 18 to 29, with 81 percent of people in that age group voting in his favor. But he was able to pull in younger voters more broadly; fully 67 percent of voters under age 45 swung his way, and they made up nearly half the electorate.

An unexpectedly large share of voters in the Michigan primary also identified themselves as liberal, with 56 percent using that moniker. Among those voters – the core of Sanders’s base – he won by more than 8 points.

In addition, voters identifying themselves as independents turned out in huge numbers, comprising 28 percent of the electorate. Nearly seven in 10 independent voters broke for Sanders, while fewer than six in 10 voters identifying themselves as Democrats sided with Clinton.

Finally, it looks as though Sanders may have cut into Clinton’s minority "firewall," giving himself an extra boost. After she won a bevy of primaries in which eight in 10 or even nine in 10 black voters swung in her favor, 65 percent of black voters in Michigan picked Clinton last night; Sanders garnered 31 percent of the black vote. That was no accident; in the days leading up to this primary, Sanders worked hard to court black voters, campaigning hard in places like Detroit and Flint with an economics-based message.

"What tonight means is that the Bernie Sanders campaign … is strong in every part of the country and we firmly believe our strongest areas are yet to happen," Sanders said in a brief election-night speech.

And he is right about at least one thing: The primary calendar next turns to other Midwestern states, including Ohio and Illinois, which could offer Sanders more Michigan-style wins.