Standing on North Broad Street on Friday as Donald Trump assured a private meeting of African American voters that he isn't a racist while angry protesters outside insisted otherwise, I wondered what would be made of all that just a few blocks away.

These are heady days for the American Political Science Association, trying to make sense of Trump's populism.

And more than 6,000 APSA members were just down Broad, gathered at the Convention Center.

Jennifer Hochschild, a Harvard University professor and the APSA president, studies race, ethnicity, and immigration as it intersects with American politics. So this was a pretty opportune time for her to visit Philadelphia.

Hochschild coauthored a book, Do Facts Matter? Information and Misinformation in American Politics, that she started in 2007 and released in 2015. During that time, she saw facts mattered less and less during each election.

What she also saw was an increase in racial polarization, even as the country elected and then reelected its first African American president.

Hochschild said people who already leaned toward racial hostility became even more racist in the last eight years.

What could be driving that? Maybe it's math.

The Pew Research Center in February said this will be the "most racially and ethnically diverse" electorate in our history. Thirty-one percent of voters will be minorities, up from 29 percent in 2012.

Hochschild says that may be a "demographic tipping point," akin to the racial strife that accompanied the desegregation of schools in '60s and '70s.

"We're at a point where there are so many minorities that whites who are inclined to feel defensive or anxious are, in a way a decade ago they didn't need to be," she said. "The hopeful story is a decade from now they won't need to be because they will have discovered the world hasn't fallen apart."

Enter Trump, with potent populism pitched precisely at white voters in a way that has enraged Black Lives Matter and immigration activists.

I stood on North Broad Street surrounded by that rage for hours. If racism is on the rise, rage is coming along for the ride.

Trump must know it. And he, or the people managing his campaign, must know that rage cuts not just into his chance for votes from minorities but also with moderate voters left uneasy by all this.

So on the Friday and Saturday of Labor Day weekend, nearly 15 months after he declared his candidacy and two months before the election, Trump felt the need to stop first in Philadelphia and then in Detroit to convince African American voters he is not a racist.

Still, Hochschild begrudgingly gave Trump high marks for sparking a larger conversation.

"Trump has done us a service by bringing to the surface a set of anxieties which both the Democratic Party and the Republican Party, and frankly us academics, didn't want to deal with," she said. "What Trump has done - I wish it was done differently - is brought that population into the center of politics. That's important. I don't like it. But it's important."

Hochschild still has hope that facts matter.

She's a teacher. She wants the country to have a "set of bedrock facts that you have to engage in."

Experience tells Hochschild that's not going to happen any time soon, as the campaign heats up even more in the traditional post-Labor Day race to the general election.

"Not in the heat of a political battle," she said of facts mattering. "It's not going to happen in the next couple of months."