Evolving views on certain issues are fine. For example, a president's views on foreign policy stances with a particular nation may evolve with circumstances in that nation, including who the leader is, the level of aggressiveness the nation puts forth, or the level of human rights abuses found therein.
Presidents might change their views on defense spending, or welfare policy, or any other host of social or political issues that might change during a presidency. (Some of these may also have a moral component, but they are primarily political issues.) We the public usually support the change if the president was our candidate, and speak out against it if he wasn't. Sometimes we might even consider the substantive nature of the change-of-position, but usually, it's about the man.
But one area where views ought not be shifting is on moral issues. One of the reasons the US Constitution requires a citizen to be at least 40 years old to be eligible to run for the presidency is so that the person might have enough age and maturity to have established a 'moral compass' that guides them through the myriad of decisions they face in office. Moral issues are never about the man, but always about the issue, because the stance on the issue defines the man (or woman) in office.
Ronald Reagan defied even his own party advisors when he called the Soviet Union the, "Evil Empire". They told him such morally decisive language would offend and be long-term destructive to the US position on various Cold War issues between the two countries. But Reagan had a moral compass, and he followed it. It was one of the reasons he was such a successful president. He turned out to be right: the USSR eventually failed as a political experiment, though not until about a year after Reagan left office. His challenge to Gorbachev to "tear down this (Berlin) wall" came to fruition in 1989. This moment may be the defining moment of his presidency as history unfolds.
I miss Ronald Reagan.
Even Jimmy Carter was willing to take a moral stand on an issue in which he believed. He issued the famous executive order prohibiting the assassination by US operatives of foreign heads of state, even if they posed a clear and present danger to US national security. I vigorously opposed this move at the time (even though I was about 16), and still think it is wrong today, both on moral and biblical grounds. But I will give President Carter credit for following his moral compass.
A sitting US President needs to have established moral values. Whether you support same-sex marriage or not; whether you think it is a doorway to equality for all or a step toward barbarianism, you should expect your president to have a clear and unequivocal position on it, and to state that position for all. I know Obama has not done that, and I don't think Romney has either.
If neither candidate for President has a clear moral position on this or any other sensitive moral issue, I'm worried. Really worried.