"It could very well be as big an issue as Roe v. Wade," says John Green, a University of Akron political scientist who studies the intersection of politics and religion. The 1973 Supreme Court decision in Roe established abortion rights and has provoked a fierce debate ever since. Gay marriage sets up a similar conflict between rights and values.
One other factor that White House aides say has had some impact: Vice President Cheney has an openly gay daughter who runs his campaign office.
http://www.usatoday.com/news/nation/2003-11-19-wedge_x.htm