Nothing, he kicked McGovern's rear end, but that isn't what Nixon will be known for. He will always be known for Watergate and to the casual non-political listener of Rush it could be construed that the casual non-political listener says to themselves, Nixon-Bush connection, "Watergate-Bush is also a liar, yada, yada, yada.."
That's why I think the Rush's Bush-Nixon connection is not only factually wrong, but also disingenuous.
I think it's a bit of a stretch to say he's trying to harm Bush electorally. He may be trying to prod him policy-wise, but I can't imagine his problems with Bush running that deep.