The element in the excerpt that suggests that stare decisis, or court precedent, was consulted is:
the reference to past cases that ruled on the topic of marriage.
In the excerpt, Justice Kennedy references significant prior Supreme Court cases, such as Loving v. Virginia, Zablocki v. Redhail, and Turner v. Safley, which illustrate the evolution of the understanding of the right to marry and how it has been treated under the Constitution. This demonstrates reliance on established precedent in reaching the Court's decision in Obergefell v. Hodges.