If Nadal can win in US Open, he will believe he can break it, and we all know he's the most motivated ambitious player around so he'll work extra to reach Federer. however Federer is not done, I believe he has 1 or 2 more slams left in him.. I believe the next year will be very critical for both... Fed's window of winning the slams is narrowing but Nadal should win a hard court slam to convince me about the record..