The Windy City Times has gone through their archives and it turns out that Obama was in favor of same-sex marriages (not unions) before he was against them. (picture after the click).
[caption id="attachment_104" align="alignleft" width="300" caption="Obama Questionaire"]
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In 1996 the gay newspaper, Outlines, asked Obama on some of his opinions. He responded to their questionaire with the note you see on the left. If you notice number 6 he clearly states that "I favor legalizing same-sex marriages, and would fight efforts to prohibit such marriages."
So I ask you Obama, do you stand by your word from 1996, or are you going to 'change with the times' and help create a world where homosexuals are second class citizens?