I've seen claims made in the news recently, but that seems tied up in the current election cycle. Is there a consensus among historians based on the evidence as to what Bill Clinton's motivation was in 1996? Can we know what political calculations he made at the time?
It seems that his advisers believed that vetoing DOMA would put his reelection in jeopardy. They believed there was already a Congressional majority and DOMA would have become law anyway overriding the veto. The article below is by one of Clinton's advisers at that time.
http://www.newyorker.com/news/news-desk/why-bill-clinton-signed-the-defense-of-marriage-act