The day after Barack Obama became the first African-American president of the Harvard Law Review in 1990, he took a phone call from Sheryll Cashin, then a law clerk to Judge Abner Mikva of the U.S. Court of Appeals for the D.C. Circuit.

Mikva by then was a “feeder judge” for Supreme Court law clerks, and Cashin told Obama that Mikva was “very interested in you,” according to a new biography of Obama's life before becoming president in 2009.

Obama's response was quick and surprising, according to the book “Rising Star: The Making of Barack Obama” by historian David Garrow, also a Supreme Court expert. “I'm flattered, but no thanks. I'm going back to Chicago,” Obama told Cashin, now a professor at Georgetown University Law Center. “I was floored,” she said. Then, as now, a path to a Supreme Court clerkship was almost a default career plan for top-tier law students at Harvard.