Sen. Tim Kaine (D-Va.), Hillary Clinton's running mate. (Gerald Herbert/AP)

Tim Kaine began his career as a fair-housing lawyer, a lesser-known detail about the Democratic vice-presidential nominee now mostly recognized for his mild-mannered dad-ness and goofy Trump impersonations.

For years he sued Richmond landlords and lenders who discriminated against blacks, which gives him deep expertise in a topic that, until now, has not figured into this presidential election. As one civil rights lawyer said to me after the Virginia senator's introduction as Clinton's running mate last month, there hasn't been such a strong fair-housing advocate on a presidential ticket since Walter Mondale, who helped write the 1968 Fair Housing Act.

Kaine tells some of this personal history in an op-ed for CNN today, recounting the story of a black woman named Lorraine who was baldly denied an apartment then offered to a white tenant. Then he ties this history to another less well-known story about Donald Trump's past:

Progress has been slow because there have always been people willing to discriminate for profit. In fact, before I started my career fighting this problem, and while my running mate, Hillary Clinton, was going undercover to expose school segregation in Alabama — our opponent, Donald Trump, was occupying himself in other ways.

Around this same time, if a woman like Lorraine attempted to rent an apartment from Trump's company, federal investigators were told that employees would have added a piece of paper to her rental application with the letter "C" on it. As the Department of Justice would later discover, "C" stood for "Colored."

Before Trump moved into the business of luxury high-rises and casinos, he helped run a rental empire built by his father in New York that catered to working- and middle-class tenants. In the early 1970s, the Justice Department accused the family of discriminating against black tenants across 39 properties the Trumps managed. The Trumps eventually signed a consent decree that required the company, among other things, to proactively list units in minority publications.

The discrimination at issue at the Trump properties is actually identical to the story Kaine tells of Lorraine in Richmond. From a deep dive on the Trump case earlier this year by Washington Post writers Michael Kranish and Robert O'Harrow Jr.:

When a black woman asked to rent an apartment in a Brooklyn complex managed by Donald Trump’s real estate company, she said she was told that nothing was available. A short time later, a white woman who made the same request was invited to choose between two available apartments.

The two would-be renters on that July 1972 day were actually undercover “testers” for a ­government-sanctioned investigation to determine whether Trump Management Inc. discriminated against minorities seeking housing at properties across Brooklyn and Queens.

The case was among the government's biggest fair-housing discrimination lawsuits at the time, Kranish and O'Harrow write. And Trump, the company's 27-year-old president at the time, showed what we'd recognize today as his defiance in the face of evidence. He called the government's accusations "completely ridiculous." The family even counter-sued the government for $100 million — unsuccessfully — for accusing it of racial bias.

The historic contrast between the Clinton ticket and Trump on this front — one fighting racial discrimination, the other accused of committing it — will probably remain a footnote to an election with new, more recent controversy arising every day. But as Kaine points out in his op-ed, the issue remains alive today, in persistent inequality in the housing market, in continued mortgage redlining and unaffordable rents that particularly burden the poor.

Housing issues, and the problems of poverty more generally, have figured little into this election and were all but absent from both parties' conventions, as the New York Times pointed out this week. "It was pretty shocking not to hear that word, housing, uttered on the main stage,” Harvard sociologist Matthew Desmond told the New York Times of the conventions.

Kaine's op-ed is notable, too, for finally broaching the topic. In it, he vows that he and Clinton will expand federal aid to public housing agencies and for low-income housing tax credits and that they'll bolster resources for fair-housing enforcement. (He does not, however, specifically call out the controversial Obama administration rule trying to disarm segregation across the country.)

He also makes another salient point: Stories similar to Lorraine's, Kaine writes, "remind us why it's so important for those of us who haven't faced barriers like these to acknowledge our privilege."