Kagan wrote this about Marshall in a 1993 law review article:
During the year that marked the bicentennial of the Constitution, Justice Marshall gave a characteristically candid speech. He declared that the Constitution, as originally drafted and conceived, was "defective"; only over the course of 200 years had the nation "attain[ed] the system of constitutional government, and its respect for... individual freedoms and human rights, we hold as fundamental today."
Marshall's speech gave particular note to the constitution's original definition of a slave as counting for only three-fifths of a person. Kagan wrote in her piece that "it was the role of the courts, in interpreting the Constitution, to protect the people who went unprotected by every other organ of government."
So Marshall critiques the Constitution for its treatment of slaves. Kagan cites the critique and praises the Court for fixing the problem. Steele slams Kagan. Nice.