African-American Democrats and white Republicans without college degrees played a huge role on Super Tuesday.
The former essentially delivered the winning margins in many states for Hillary Clinton with the latter doing similarly for Donald Trump.
African Americans have complained white Democratic presidential candidates sometimes take their votes for granted, and some white working-class voters feel neither party makes policies to improve their lives.
But if Clinton and Trump win their parties' nominations, they will have these two blocs to thank — and potentially repay in some ways politically.
According to exit polls in six Southern states (Arkansas, Alabama, Georgia, Tennessee, Texas and Virginia) that voted on Super Tuesday, Clinton didn't get more than 60 percent of the white vote in any of them.
If only white Democrats had voted on Tuesday in those states, Vermont Sen. Bernie Sanders would not have been that far behind Clinton in terms of accumulating delegates.
But the former secretary of state won more than 80 percent of the African-American vote in those six states, turning what would have been closer races if only whites had voted into complete blowouts.
In Virginia, Clinton won about 58 percent of the white vote, compared to 84 percent among African Americans. She beat Sanders by nearly 30 points there overall.
In contrast, Clinton's victory was much closer in Massachusetts, which has a very small black electorate. Sanders won in in Minnesota and Colorado, two other places where African Americans were not a huge segment of the voters.
Tuesday continued a pattern for Clinton: she is very reliant on the black vote. In the two states with tiny black populations that started the primary process, Clinton barely won Iowa and then lost soundly to Sanders in New Hampshire.
But exit polls suggest that in both Nevada and South Carolina, her overwhelming leads among black voters were instrumental to her victory.
Similarly, Trump, in the states he won, had narrow advantages among Republicans with college degrees. He lost the vote among more educated Republicans in Arkansas (Texas Sen. Ted Cruz) and Virginia (Florida Sen. Marco Rubio) even while winning those states. (Cruz won Oklahoma and Texas outright and carried both more educated and less educated voters in those two states).
But among Republicans without college degrees, Trump trounced his opponents. For example, in Massachusetts, Trump won 39 percent of Republicans with college degrees, but a whopping 59 percent of those without. In Virginia, he won 27 percent of those with degrees, compared to 44 percent of those without.
Clinton and Trump's successes with these blocs are not accidents. Clinton has aggressively appealed to African Americans in her campaign, for example arguing the water crisis in Flint, Michigan, is partly the result of local officials not caring sufficiently about the residents of a low-income, majority-black town.
While campaigning in South Carolina last week, Clinton was endorsed by several African-American mothers whose sons or daughters died following controversial altercations with police, including the mothers of Eric Garner and Sandra Bland.
Trump meanwhile has argued that the political establishment of both parties is not doing enough to stop U.S. jobs from going overseas. He has been the most vocal Republican candidate in opposing international trade agreements and arguing that immigration depresses the wages of American workers already here. These are clear appeals to voters who may be struggling in today's global economy.
And these two voting blocs may have particular interests in backing Clinton and Trump. In interviews, African-American voters praise Clinton for her long political experience and her decision to serve in the cabinet of President Barack Obama. And black voters, particularly older ones, say they view Sanders' promises of a political revolution unrealistic and don't think a self-proclaimed socialist could win a general election.
White working-class Republicans may correctly perceive candidates like Rubio and Cruz as closer to the political establishment and Trump as an outsider more likely to oppose international trade agreements, which presidents of both parties have supported in the past.
This story first appeared on NBCNews.com.