Week seven of Melissa Harris-Perry’s introductory course in African-American studies at Tulane University includes a lecture about “the hollow prize” — a theory that African-Americans tend to be elected as mayor only after a city has tipped into economic decline.

One day last summer, when Ms. Harris-Perry was filling in for Rachel Maddow on MSNBC, she recast the class lecture as a television segment, invoking Detroit; her adopted home, New Orleans; President Obama; and tax policy.

“I’ve given that lecture a million times — a million times,” Ms. Harris-Perry said in a recent interview. “But I do it once on Rachel’s show, and it was everywhere the next day. It was up on Web sites, people were e-mailing me — that, for me, was a really clear indication of how powerful television is.”

Now, MSNBC is about to introduce a progressive talk show called “Melissa Harris-Perry” on Saturday and Sunday mornings. Ms. Harris-Perry will be the only tenured professor in the United States — and one of a very small number of African-American women — who serves as a cable news host....