It didn't work the last time because politicians like Ted Kennedy gutted funding for enforcement. The vote on the fence the other day is proof they're ready to do it again. Until they secure the borders and make a real commitment to enforce the laws there's no need to pass anything at this time.
I highly suspect that if the House agrees to a compromise that funding will not be a problem. They in fact will demand it as to any security measures they will put on the border or else where