sparky & Nick8:
I'm not sure what some of these posters want Obama to do. He doesn't have a magic wand to change state laws or people's minds. Presidents have nothing to do with gay marriage - unless he wants to propose a federal constitutional amendment.
Bush tried a constitutional amendment against gay marriage --- both houses of Congress need to muster up a two-thirds majority (and that's the easy part; after that, 75% of the states have to ratify the bill). Bush could not even do the easy part of getting a bill passed in Congess even when he had republican majorities.
(We got great speeches on the Senate floor, though, debating the issue. I remember former senator Rick Santorum compared gay sex to "man-on-dog" sex... then arguing that, what's next? A man marrying his goat?)
"Don't ask, don't tell" is a federal issue. Obama could insert himself into that topic.
The U.S. Supreme Court could insert itself into the gay marriage debate. But I'm not sure I'd want a case taken up just yet. I have a feeling all the conservatives - Thomas, Alito, Scalia and Roberts - would vote against it. And we'd then have to pick up all of the remaining votes.
With reference to black and white marriage, there was a whole series of precedents. As far back as 1883, in "Pace v. Alabama", the U.S. Supreme Court ruled that convicting an Alabama couple for having interraical sex did not violate the 14th Amendment. -- So, interracial sex was a felony. Though adultery was only a misdemeanor as long as it was done within your race.
Virginia had passed the "Racial Integrity Act of 1924" which required that a racial description of every person be recorded at birth, and made marriage between white persons and non-white persons a felony.
A lot of states then made similar bans. Anti-interracial marriage laws were not challenged in the U.S. Supreme Court until 1967 with "Loving v. Virginia". Mildred Loving was an african-american, also part Native American, woman who married Richard Perry Loving in the District of Columbia - they left Virginia to evade the "Racial Integrity Act". When they returned home to Caroline County, Virginia, they were charged with violation of the ban. They were caught sleeping in their bed by a group of police officers who had invaded their home in the hopes of finding them in the act of sex (another crime). In their defense, Ms. Loving had pointed to a marriage certificate on the wall in their bedroom. That, instead of defending them, became the evidence the police needed for a criminal charge since it showed they had been married in another state. Specifically, they were charged under Section 20-58 of the Virginia Code, which prohibited interracial couples from being married out of state and then returning to Virginia.
At any rate, the ACLU became involved. And "Loving v. Virginia" finally overturned all those antiquated laws in 1967. But it was a long, long road.