Can vulnerable Democrat Senators really separate themselves from Obama on gay marriage?

According to The Hill newspaper, many Democratic Senators in swing states are distancing themselves from Obama on gay marriage.  But here is the problem.  This issue is going to be decided by the Supreme Court.  Does anyone doubt that Obama won't appoint another very liberal member of the court who would rule that there is "no rational basis" for ruling that marriage must be between a man and a woman?