In fiction and nonfiction, the author Danzy Senna focusses on the experience of being biracial in a nation long obsessed with color lines. Now that Kamala Harris is the Democratic candidate for President, some of Senna’s concerns have come to the fore in political life. Donald Trump attacked Harris as a kind of race manipulator, implying that she had been Indian American before becoming Black for strategic purposes.  The claim was bizarre and false, but Senna feels that it reflected a mind-set in white America. “Mixed-race people are sort of up for debate and speculation, and there’s a real return to the idea that your appearance is what matters, not what your background is or your identity,” she tells Julian Lucas, who wrote about Senna’s work in The New Yorker.  “And if your appearance is unclear to us, then we’re going to debate you and we’re going to discount you and we’re going to accuse you of being an impostor.”  Senna talks about why she describes people like herself and Lucas using the old word “mulatto,” despite its racist etymology. “The word ‘biracial’ or ‘multiracial’ to me is completely meaningless,” she says, “because I don’t know which races were mixing.  And those things matter when we’re talking about identity.”  Senna’s newest novel, “Colored Television,” follows a literary writer somewhat like herself, trying to find a new career in the more lucrative world of TV.