James Taranto of the Wall Street Journal throws a bucket of cold water on the notion that Justice Anthony Kennedy is a "sure thing" for gay marriage:

"...Back in 2010, this column made essentially the same prediction [that Kennedy would support gay marriage], and on the same grounds. Now we're not so sure. It seems to us that Kennedy's "powerful, eloquent and compelling" language in these two rulings--as well as Justice Antonin Scalia's language in dissent, equally deserving of those adjectives--makes them seem more sweeping than they actually were, especially the first of the two, Romer v. Evans (1996). 

Romer was the case that struck down Colorado's Amendment 2, a ballot measure amending the state's constitution to bar laws or policies protecting homosexuals from discrimination.

... As it turns out, however, in 1997 a federal appeals court drew precisely that distinction in allowing to stand a law similar in many ways to Amendment 2. The following year the Supreme Court let the lower court's ruling stand, as the Cincinnati Enquirer reported at the time...

... Kennedy may be as activist and results-oriented (on this matter, anyway) as Erwin Chemerinsky thinks. His moralizing rhetoric in Romer and Lawrence certainly has led us to think so. But there's nothing in the legal logic of those cases that makes a constitutional right to same-sex marriage inexorable.