Bernie Sanders won even bigger than expected in the Wisconsin presidential primary Tuesday night, marking his sixth straight victory over Democratic rival Hillary Clinton. Though he still lags behind the former secretary of state in the overall delegate count, he's picked up significant momentum and the win from a big state like Wisconsin keeps it going.

After fighting neck and neck with Clinton and losing more than six contests to her before this stretch, how exactly did the Vermont senator pull off these recent wins?

Much of Sanders’ success in the past six nominating contests comes down to demographics. Most of the last six states he won — including Idaho, Utah, Washington and Wisconsin — have overwhelmingly white populations and are some of the most liberal states in the country, according to Gallup research. Sanders does best among white, liberal voters, and even better among young, white, liberal voters.

He also does well in states that hold caucuses, because those contests reward candidates with die-hard supporters. Caucuses involve giving speeches, making the case for your candidate, and can often take much longer than regular primaries, which means participants have to be enthusiastic enough to stick around.

When we look at the states Sanders has won recently, Idaho is 93.5 percent white, Utah is 91.4 percent white, Washington is 80.7 percent white and Wisconsin is 87.8 percent. On top of that, states like Wisconsin and Washington have significant college populations, which turned out heavily for the Vermont senator.

Sanders was the heavy favorite in most of these contests, which led Clinton to spend less time and money campaigning in the states. As voters in Wisconsin headed to the polls on Tuesday, Clinton remained in New York, holding a town hall event in the afternoon and a fundraiser in the evening, ahead of the Empire State's April 19 primary..

But demographics are not the only reason for Sanders’ success. After all, he also won in Alaska (which is just 66.9 percent white) and Hawaii, with one of the lowest white populations in the country at 26.7 percent. More clarity can be found in some of the exit polls from the recent contests.

In Wisconsin, for example, CNN exit polls showed that the economy and income inequality topped the list of issues Democratic voters cared most about. Sanders has built his campaign on a foundation of talking about income inequality and changing America's economy, so it's no surprise that this helps him. Among voters who listed those issues as most important, Sanders beat Clinton 54-46 percent and 66-34 percent, respectively.

A full third of Democratic primary voters in Wisconsin also said the top quality they wanted in a candidate was honesty, an issue that has continued to plague Clinton throughout the primary season. Unsurprisingly, Sanders won 83 percent of voters who said they wanted an honest candidate. Another 30 percent of voters said they want a candidate who cares, while just 9 percent listed electability as their top priority.

There were few exit polls from the other states that Sanders has won recently, but the concerns expressed by Wisconsin voters echoed ideas expressed by voters in other states where Sanders did well this cycle.

After these wins, Sanders has closed the gap in the delegate count between him and Clinton, but he remains about 250 delegates behind the former secretary of state. Next up is the Wyoming Democratic caucus on April 9 and then the all-important New York primary election on April 19. Sanders hopes to challenge Clinton in her adopted home state, and while it will be an uphill battle, the momentum and funds Sanders gains from this streak of wins is likely to help him as he campaigns in New York over the next two weeks.