Today in Public Discourse, Carson Holloway sorts through Justice Kennedy's arguments relating to same-sex marriage:

...Kennedy's past opinions on related questions seem to indicate his openness to the constitutionalization of same-sex marriage, but the evidence is nevertheless equivocal. Kennedy authored Lawrence v. Texas, in which the Court struck down Texas's law against homosexual sodomy, and in that opinion Kennedy permitted himself to wax somewhat indignant about the supposed irrationality of moral disapproval of such conduct.

On the other hand, he also used that opinion to assure the nation, in the Court's name, that the issues in that case had nothing to do with the question of same-sex marriage. As a result, Kennedy might not be so favorably disposed to a constitutional claim for same-sex marriage, since the advance of that cause has been for the last decade linked to the work of state courts that turned Lawrence's reasoning precisely to the end that Kennedy and the Court disclaimed.