[Mary L. Dudziak is the Judge Edward J. and Ruey L. Guirado Professor of Law, History and Political Science at the University of Southern California. Her most recent book is "Exporting American Dreams: Thurgood Marshall's African Journey" (Oxford University Press, 2008). She is writing a book about law and war in 20th-century U.S. history.]

Republican senators this week pressed Supreme Court nominee Elena Kagan on the degree to which her views mirror those of her mentor Justice Thurgood Marshall, whom Kagan clerked for in 1987-88.

You might have thought Marshall himself was before the Senate. Sen. John Kyl of Arizona opined in his opening statement Monday that Marshall's judicial philosophy "is not what I would consider to be mainstream." Sen. Jeff Sessions of Alabama concurred, calling the landmark civil rights-lawyer-turned-judge "a well-known activist."

Kagan reminded the senators that if confirmed "you will get Justice Kagan. You won't get Justice Marshall."

There's an irony here. While Kagan and Marshall surely have important differences, there is something they have in common, but it's not what Kagan's Republican questioners have in mind. During confirmation hearings, both were criticized not only for their own ideas, but for those of another....