By Patrick Murray

The story of the 2020 primary has been that Joe Biden does well among older voters, moderates, and black voters.  Bernie Sanders counts younger voters, liberals, and Latinos among his key backers.

We have exit poll data from 16 states so far this cycle – nine won by Biden, six won by Sanders, and one yet to be called.  Analysis of key group support across these states reveals that victory is not just a matter of which groups supported each candidate, but by how much.

Biden was backed by just over half of voters aged 45 and older in the states he has won so far, but he only managed to get 3 in 10 of this group’s support in the states won by Sanders. Similarly, Biden won half the vote of moderate and conservative voters where he was victorious, but only one-fourth in the states he lost.

In the states that landed in Sanders’ column, he won a clear majority of voters under 45 years old. That group’s support dropped to less than half in the states he lost to Biden. In the states Sanders won, he got the backing of 4 in 10 liberals, but only a third of this group in states Biden won.

Biden’s black support has been a key factor in his surging campaign this week. Biden has emerged victorious when he was able to claim the backing of 6 in 10 black voters on average, regardless of the share of the black electorate in any given state. He lost states where his support among black voters was about half that level. When Sanders was able to win about half of the Latino vote, he tended to win the state as well, but he lost states where his Latino support was less than 4 in 10.

While all these demographic groups have been identified as key blocs for the two candidates in pre-election polls over the past year, the way white voters have divided their support has also proven to be a critical factor in Biden’s comeback.  In states he won, Biden tended to claim more than one-third of the white vote. His share of the white vote was about one-fifth in states he lost. The white vote has not been as decisive for Sanders – he has won about the same proportion of this group in states he has won and states he has lost.

The one state that really tested these countervailing racial dynamics is Texas, which has significant numbers of both black and Latino voters. Biden got 58 percent of the black vote in Texas, only a few points shy of his average black share in the states he won.  Sanders won only 39 percent of the Latino vote there, which is on par with the average margin in states he lost. The two candidates split the white vote (30% for Sanders and 28% for Biden), but it was the differential vote shares between black and Latino voters that put Biden over the top. And this linkage between key group vote share and outcome held even though there were many more Latinos than black voters in yesterday’s Democratic electorate in Texas.

Now, of course, there are exceptions to these overall trends. Biden won Massachusetts, for example, despite low support among the small group of black voters in that state. But the overall analysis of the exit polls to date suggests that the threshold of support within each candidate’s key groups may be more critical in determining the outcome than the share each group represents in any given state’s electorate.  We will see if this trend continues in the diverse states up for grabs in the coming weeks.

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Notes: Thank you to the NBC News Decision Desk for access to the exit poll data.

Biden states = AL / MA / MN / NC / OK / SC / TN / TX / VA

Sanders states = CA / CO / IA / NV / NH / VT

Iowa is a Sanders state based on initial preference vote. Maine’s winner is uncertain.