As more data emerge to explain former Vice President Joe Biden’s stunning victory on Super Tuesday, there are two clear demographics that propelled him: African-American voters and suburban voters with college degrees.

It’s a coalition that helped moderate Democrats flip seven governorships, two Senate seats and about 40 House districts (the newly Democratic suburbs alone would have secured a House majority) from red to blue in 2018. African-Americans have long made up a core of the Democratic voting base, but many of Mr. Biden’s college-educated, suburban supporters are right-leaning independents or moderate Republicans who supported candidates like John McCain and Mitt Romney. They don’t want to re-elect Donald Trump. And they’re willing to cross over to vote for a Democrat — a moderate and mainstream Democrat.

These voters might not identify with the “Never Trump” group of conservatives who vociferously oppose the president. But in practice, that’s who they are. They often voted for Republicans in the past and are now firmly anti-Trump. These voters can create winning margins for Democrats in swing states like Michigan, Pennsylvania, Arizona and North Carolina in the general election.

Their numerical strength was on full display on Super Tuesday in the Virginia and Texas suburbs, which saw 74 percent and 87 percent higher voter turnout, respectively, than four years ago. These de facto Never Trumpers also showed up in large quantities in the suburbs of Charleston, S.C., where 58 percent more people voted in the Democratic primary last Tuesday compared with 2016. And they pulled the lever overwhelmingly for Joe Biden. In Iowa last month, while Democratic turnout was down from 2016 throughout the rest of the state, it spiked 38 percent in Dallas County — the far suburbs of Des Moines that had been stalwart Republican country not long ago.