Hillary Clinton speaks to her supporters during her Primary Night Event at the Palm Beach County Convention Center . (Photo by Joe Raedle/Getty Images)

Coming into Tuesday night, observers wondered if Hillary Clinton would suffer the same fate in Ohio as she did last week in neighboring Michigan. In Michigan, you'll remember, Clinton was far ahead in the polls but ended up losing to Bernie Sanders narrowly. Would Ohio, a Rust Belt state with broadly similar demographics, be another loss?

It would not. Shortly after polls closed, the Associated Press called Ohio for Clinton; as of writing, she leads by a wide margin. What was the difference?

White voters.

We've been talking for months about how non-white voters are Clinton's fail-safe. Black voters in the Deep South gave Clinton massive margins of victory in those states, helping to power her huge delegate lead. But in Ohio, it was white voters. In both Ohio and Michigan, about a fifth of the electorate was black, according to preliminary exit polls reported by CNN. In both states, Clinton won the black vote by about 40 points. But in Ohio, she ran about even with Sanders among white voters. In Michigan, she trailed him by 14 points with whites.

In other words, the old calculus -- more black voters means a Clinton win -- was back in effect, because she wasn't hammered by whites.

In the five states that voted on Tuesday, preliminary exit poll data shows that in the three which were called early, Clinton did reasonably well with white voters and very well with non-white voters. In the two where news outlets couldn't call the race as easily, Clinton is getting beaten badly among white voters.

We can look at the same data as a function of the overall vote, as above. In places where the support from whites is about the same between the two, Clinton in winning.

We've noted before that the racial composition of the electorate is the main factor that changes from state to state on the Democratic side. That's true. But the balance of support for Clinton from white voters is also important, as Ohio shows.

It's critical to note, by the way, that even a narrow loss in Ohio wouldn't have meant much for Clinton. Because the Democratic contests are all split proportionately, Clinton's giant win in Florida essentially guaranteed that she'd end the night with more delegates than Sanders. If the margin in Ohio holds, that's icing on the evening's cake. If Sanders wins Illinois and Missouri, as it currently appears he could, the states' delegates are essentially a wash.

Clinton's delegate lead coming into the night was already larger that was Barack Obama's at any point in 2008.

That margin will grow dramatically, thanks, for once, to white voters.