As to 1, I believe that it is united America against a minority of people, which the government is not supposed to do. I personally believe that the state has no right to deny a marriage to a couple just because they're gay. At the same time, I understand that many, many people believe marriage is a sacred institution. My belief is that the state should not deny this right but the churches do not have to marry the people themselves.
As for 2, there is no clear mandate. With such a close margin of win, it is clear that many people do not agree with G.W. Many of my friends (most of whom are conservative) would have voted for Kerry except they voted on the "moral" issues, that being gay marriage, abortion, etc., although they preferred Kerry on economic issues and the Iraq war. <a href="http://www-personal.umich.edu/~mejn/election/">A map</a> of the election results adjusted for population density and voter percentages showing that there really isn't that much of a mandate.