JUDY WOODRUFF:

Now what we know about Donald Trump's taxes, what we don't know, and how his real estate business could be affecting his tax bill.

That subject led to one of the more memorable exchanges of this week's presidential debate.

Our economics correspondent, Paul Solman, sat down with a Pulitzer-Prize winning investigative journalist, David Cay Johnston, who's been reporting on Trump since the late '80s. He's also the author of a bestselling book, "The Making of Donald Trump."

It's part of our weekly series Making Sense.