So what explains the different results in the Kentucky and Texas cases involving the Ten Commandments? Justice Breyer provided the decisive 5th vote in each case, so we must consult his opinion concurring in the judgment in the Texas case (beginning at page 23) for the answer.
For “difficult borderline cases” that are “fact-intensive,” there is Breyer tells us, “no [Establishment Clause] test-related substitute for the exercise of legal judgment.” That judgment “is not a personal judgment” but “must reflect and remain faithful to the underlying purposes” of the Religion Clauses and “must take account of context and consequences.”
The particular factor that Breyer finds “determinative” in this case—but don’t jump to the foolish conclusion that anything similar might be determinative in any other case—is that “40 years passed in which the presence of this monument, legally speaking, went unchallenged.” By contrast, the Kentucky displays had a “short (and stormy) history.” And “a more contemporary state effort to focus attention upon a religious text is certainly likely to prove divisive in a way that this longstanding, pre-existing monument has not.”
In short, it would seem, under Breyer’s view, American citizens today lack the power that their parents and grandparents had to have our governments affirm, acknowledge, and encourage respect for our religious heritage.