Although a decent number of anti-same-sex marriage activists are pushing for a federal constitutional amendment to define marriage, there isn't much momentum for such an effort.

What makes you say this, tho? Nobody even saw Prop 8 coming. Most people thought, oh what a silly thing, it will fail on its own don't pay their little smear campaigns any mind. And then it passed. And then it was upheld.

I think anti-same sex marriage activists are counting on us to think there isn't much momentum for their cause. Obviously they know something we don't.