In his most important win to date, Bernie Sanders tonight won the Michigan Democratic primary, according to AP projections. Though he remains a good deal behind Hillary Clinton in total delegate count, his win in the Wolverine State has changed the race for the Democratic nomination.

For weeks, Clinton has been racking up wins, mostly in Southern states. Sanders and his aides have stressed, though, their belief that he could do much better in Northern and midwestern states. Tuesday’s result gave credence to that belief, and could well propel Sanders in other states in the region: Ohio, Missouri, and Illinois both vote next week. Wisconsin votes in early April.

More than anything, though, this vote gives Sanders a legitimate reason to stay in the race. If he’d lost, which the polls had indicated he would, it would have been difficult for him to make the case that the voters wanted him to keep up his challenge to the Clinton machine. He will likely be able to use this win to get another round of fundraising, as most of his donors are individuals who haven’t maxed out their donation totals; if they gave $10 in October, he can ask them to give another $10 now. And given the general enthusiasm of Sanders voters, it’s a good bet a lot of them will.

Sanders still faces an uphill battle to the nomination. Hillary Clinton has polling leads in several key states. She has the lion’s share of super delegates. And because Democratic delegates are divided proportionally, she still gets votes from the states like Michigan where Sanders barely wins.

But don’t discount the win for Sanders. It shows that his message of economic, left-wing populism has resonated with Democratic voters. And it shows that Hillary Clinton is going to have to fight for the Democratic nomination.