Did the twins' appearance tonight turn any voters away from the President?
Doubtful.
Did they turn some toward the President?
Possible.
Nothing wrong with their being there at all.
My wife and I really cringed at the Bush Twins. I think they did hurt the president, in the regard that they perpetuated the (democratic) conventional wisdom that GWB is "dumb". Their daughters certainly came off that way.
It was an absolutely dreadful performance.