"President Obama endorsed gay marriage in an interview Wednesday. The president has described his views on gay marriage over the past few years as “evolving,” but many believe he was just waiting for public opinion to catch up with him. Can someone's moral principles really evolve?

"Yes. While some of the growing national acceptance of gay marriage is the result of turnover—as  older, more socially conservative people die off—there has been a significant amount of mind-changing among members of the American public."

Slate

Morality is not simply a peer reviewed process. It is a fact of nature. Morality is those actions and behaviors that lead to the good health and well-being of individuals and communities.  

 

Insofar as homosexuality is a moral behavior, or not, depends on how it is practiced and what its results are for the individuals involved. If the result is rectal cancer, rectal injuries, the spread of infectious disease, the degradation of human character, the cultural disruption of a society, or other negative effects on the health and well-being of individuals and communities, then homosexuality is immoral. To the extent that homosexuality contributes to the good health and the well-being of individuals and communities, then it is a moral behavior.  
 
In the end, the morality of homosexuality will be determined by its cost or benefit to human civilization, not by a liberal or conservative President.